Does transubstantiation occur when the Eucharist is received by one barred from sacraments? If someone is banned from receiving the sacraments through interdict or excommunication but does so anyway (perhaps they go to a different parish where their status is not known) does the sacrament still take effect?  Specifically, if someone is barred from receiving the Eucharist, does transubstantiation still occur?

It's my understanding (and agreed with in this question) that the transubstantiation occurs when the priest says the words of instantiation – that is, before they are received by the potential excommunicatee.
The Bible itself implies that the occurrence of the act of transubstantion is independent of the worthiness of the recipient.
In 1 Cor. 11:27, it is written,

27 Wherefore, whoever eats the bread or drinks the cup of the Lord unworthily shall be guilty of the body and the blood of the Lord.
ΚΖʹ ὥστε ὃς ἂν ἐσθίῃ τὸν ἄρτον ἢ πίνῃ τὸ ποτήριον τοῦ κυρίου ἀναξίως ἔνοχος ἔσται τοῦ σώματος καὶ τοῦ αἵματος τοῦ κυρίου NA28

If a man was unworthy, then why would he be guilty of the body and blood of the Lord if transubstantiation did not occur on account of his unworthiness? Yet, he is guilty for the very fact that what he consumed and drank was the very body and blood of the Lord Jesus Christ despite unworthily receiving it.
Furthermore, if he only consumed mere bread and wine, why would he be guilty of anything? Unworthy individuals eat bread and drink wine all the time, e.g. unbelieving Jews. Did the apostle Paul really intend to say that all unbelieving Jews are guilty of the body and blood of the Lord for eating bread and drinking wine on, say, the Sabbath? I hardly think that was his point. He was directing his comments to those that participated in the Lord's Supper/Eucharist/Communion because that bread and that wine that is received during the Eucharist becomes the body and blood of our Lord Jesus Christ, unlike common bread and wine that is received by others, elsewhere.