Did John Wycliffe accept extreme unction? According to Bruce Shelley, in Church History in Plain Language, John Wycliffe, the early dissident in Catholicism, accepted the sacrament of extreme unction:


  He retained belief in purgatory and extreme unction


However, this seems to contradict what Shelley writes next:


  he admitted that he looked in vain in the Bible for the institution of extreme unction [...] The standard Wyclif used to judge the Roman Church was the teachings of Scripture.


I have a feeling that Wycliffe's views on extreme unction were a bit more nuanced, or at least confusing, than that he simply accepted it.  So:


What did Wycliffe believe about extreme unction?


If he accepted it, on what basis did he do so?  Biblical (contra Shelley)? Or non-biblical?
If he rejected it, how did he explain James 5:14–15?

Do his writings indicate that his views changed during his life?
To answer your question about 'extreme unction' Gillets summarizes it best under the phrase 'qualified sense'


  The seven sacraments of the church were all admitted, though in a qualified sense, by Wickliffe. It is evident that his exposition of their significance would strip them of all that peculiar importance which was attributed to them by the prevalent superstitions of the age. (the LIFE AND TIMES of JOHN HUSS; or, the Bohemian Reformation of THE FIFTEENTH CENTURY by E. H. GILLETT, p64)


it seems clear that he opposed the idea 'in the way it was administered' but not in the overall entitlement of being called a sacrament. In a book where speakers had a talk about these subjects called "De conversation ecclesiasticorum" he directly addresses the matter:


  The names of these speakers are Alithia, Pseudis, and Phronesis—or Truth, Falsehood, and Wisdom. The opinions and reasonings of Alithia, accordingly, are to be regarded as those of Truth; those of Pseudis as being the contrary of truth; while in the person of Phronesis, Wycliffe himself speaks.
  
  XVIII
  OF EXTREME UNCTION
  Alithia. You have said quite enough on this subject, brother Phronesis; but inform me, I pray you, somewhat concerning the last sacrament, which is called extreme unction. It has its foundation in the passage, James 5, “Is any sick among you? let him call for the elders of the church; and let them pray over him, anointing him with oil in the name of the Lord: and the prayer of faith shall save the sick, and the Lord shall raise him up; and if he have committed sins, they shall be forgiven him.”
  
  Phronesis. This foundation for that sacrament does not appear to be adequate. For the faithful might urge with sufficient reason, that this holy apostle does not specify the last sickness, but merely says that consolation should be administered by the presbyter when any one is sick; and as it is in the nature of oil, in those parts of the world, to promote the health of the body, so he mentions this anointing; not that the oil affects the soul, but the prayer of a devout priest poured forth, hath a healing effect, so that God helps the sickness of the soul. If that bodily anointing had been a sacrament in the sense in which it is now represented, Christ and his apostles would not have been silent respecting its promulgation and due administration. Nevertheless, I grant you that this corporal anointing is to some a sacrament, other things being equal; but it is then necessary that the presbyters should heal the sick with their own devout prayers. Still, beware, lest through too light a temper, you understand the words of the apostle imperfectly.
  
  You may possibly err so far as to believe, that the mere fact that a priest has prayed for a sick man will be sufficient to remit any guilt that may attach to the latter. But many have been sick, and been anointed, who have, nevertheless, been doomed to everlasting condemnation. For it is not to be believed, that, insomuch as a priest so doth, his prayer of faith will save the sick, for then it would be a part of the faith of the church to believe, that whoever in his last moments should receive the sacrament, would be saved by faith in Christ, and this sacrament would then be the most necessary of all, for the recipient of the others may be finally impenitent, and be lost,—but so, without a doubt, may he be who receives this sacrament.
  
  Thus in the sacrament of baptism, in that of confirmation, and in all the rest, hath Antichrist invented unauthorised ceremonies; and to the burden of the church, without warrant from Scripture, hath heaped them on subjected believers. But other necessary sacraments he has overlooked, as is seen in respect to the seven works of spiritual mercy, which ought to be a sacrament in the esteem of believers, and especially of priests. But this sacrament, though very necessary, inasmuch as it has no temporal gain going along with it, and is irksome to those in high places, is faithlessly neglected.
  
  Whence it appears to me, that those who institute such private orders, and send forth such general rules, to cause sacraments of this nature to be universally received by those who are subject to them, blaspheme God, especially when God is pleased to save many without their receiving this sacrament. How like Antichrist is this presumption, for a prelate to assert, and without foundation maintain, that no one will be saved without partaking of a sacrament of this sort!
  
  But whether a rich man, thus anointed, is permitted subsequently to recover, and whether the priest ought to have a certain knowledge, that the man so anointed will not survive, and whether this sacrament of extreme unction ean be repeated, is a matter of doubt with many. But I leave it to the weak, uselessly to protract difficult questions of this nature. I merely state one thing as probable,—that a man thus sick, and thus anointed, and afterwards convalescent, cannot again receive the sacrament of extreme unction. (TRACTS AND TREATISES of
  JOHN DE WYCLIFFE, D.D.,THE REV. ROBERT VAUGHAN, D.D., P182)


So I think you can judge for yourself. He seems to oppose extreme unction zealously, in the way it was used.

From what I can tell the focus that Wycliffe held was in opposition to the authority of the Pope, more than say 'justification by faith' which was Luther's focus. However Wycliffe holds Augustinian ideas that seem to indicate that he felt real grace and predestination is what saved a man. However, it was not as focused and or nearly developed as in the case of Luther. His opposition to the Pope and corruptions of many of his representatives is very lively though. Unfortunately, there does not seem to be as much clear record of his writings either, compared to the large volumes available for Luther.