Would it compromise the strength of an alconite fly rod guide to shorten the foot a bit?

I doubt it would compromise the strength of the guide, but the less area you have for wrapping, the easier it will be for the guide to loosen or pull out of the wraps. That's where the real danger lies.

As in most things, moderation is the key. If you have an application where you simply do not feel you need the length you have in stock form, then shortening it a tad may be just fine. You'll know if you have taken off too much, as the guide won't stay put under pressure or over time.

.....................

Also, definately use a locking wrap if you shorten the guidefoot. This will prevent the guide from loosening or coming out.