So, very simple croping test with fitfiletools : yes it crops the tracks, the time and the distance, but it kills any ascent/descent data. Maybe it assumes that app will recalculate those values (which is the case for many of them, but not SA : if no total_ascent in fit file, nothing in SA).
It is no criticism, just facts, i imagine that these file are nicely digested by Stava, but for pure and complete fit files, these are two options i won’t use as is (and i would love to do it, it is easy and convenient).
The other fact is that i search quite a lot for easy fit file manipulators that keeps some key values at the end, and i can’t find on that makes all (golden cheetah is good, but first fit export is not OK for SA, missing session message, etc…).