Do any young earth creationists believe that a change to the earth's axis tilt was God's way of shortening human lifespans? Scripture tells us in Genesis 6:3 that God saw fit to shorten the lifespan of mankind. He did something that dramatically reduced humans years from close to a thousand years (Methusala) to 100 or less. Some speculate that the flood opened the earth's atmosphere up to greater UV light and changed atmospheric pressure and those things changed the environment thus shortening human lifespans. 

Recently I had a interesting dialogue with a Christian who had been taught that the Creator accomplished the goal of shortening lifespan by tilting the earth from original setting to a more extreme setting that changed "normal" to a new "Normal," which caused the dramatic climate changes and led to a much different  habitat for humanity and shortened the life expectancy. This was partially supported by scientists quoted here who theorize that the orbit and tilt of the earth causes emergence and extinction of mammals in 2.5 million year cycles.

I know the YEC Christians have much to say about the meanings of Genesis history. Have any YECs ever written about the effect of the earth's tilt on the way lifespan or other environmental decline occurred?
As indicated in this overview of YEC theories regarding the decline in lifespans, environmental changes (such as might be caused by a change in the earth's axis tilt) are not typically cited as a significant cause of the decline in human lifespans.  Environmental changes in general are seen as having only a minor effect, if any, due to the continued long life of Noah and his immediate descendants:

All positions which attempt to explain the ‘lifespan drop’ in environmental terms have another bit of data to explain, and that is the temporary persistence of longevity after the Flood. Noah was 600 at the time of the Flood, but lived another 350 years afterwards, in the post-flood atmosphere! Even in pre-Flood terms, Noah was already of moderately advanced age. One would presume that, if the post-Flood atmosphere/environment has such devastating effects on us now, then because Noah would have been instantly exposed to these same effects, it should have cut his life short much more rapidly.1 [emphasis in original]

That said, some YECs nonetheless argue that there was a change in the tilt of the earth's axis caused by some catastrophic event in the past, perhaps in association with Noah's flood. This shift is cited as evidence for YEC geomagnetism theories, such as magnetic reversals; Noah's flood itself; and methods of archaeological dating (since many ancient events are traditionally dated older than 4000 BC, the approximate year of the creation of the world according to many YECs).2
However, these theories are not directly connected to the decline in human lifespans, nor are they widely accepted even among Creationists.  Creation Ministries International writes:

Some creationists believe that a change in axial tilt (but not from the vertical) started Noah’s Flood. But a lot more evidence is needed and this idea should be regarded as speculative for now.3

Summary
Some Creationists do argue for shifts in the earth's axial tilt.  However, this shift is not directly connected to the change in human lifespans; rather, it is seen as evidence for YEC theories of geomagnetism and archaeological dating.  That said, many YECs regard axial tilt theories as speculative and not particularly likely.


Carl Wieland, Decreased lifespans: Have we been looking in the right place? (Creation Ministries International)
The Dodwell Hypothesis is the best-known example of this.  Bill Overn defends and applies the hypothesis in his paper, &quot;The Tilt of the Earth's Axis.&quot;  Paul D. Ackerman suggests that Dodwell's Hypothesis explains the cause of the Flood (an asteroid striking the earth).
Arguments we think creationists should NOT use.  See also Danny Faulkner's rejection of Dodwell's hypothesis (Answers in Genesis).