cutting the material shouldn't give you any issues.
Generally speaking, the "heat affected zone" is an issue with welding/temperatures.
There is lots of information on this subject, most I agree with.
Carrol Smith books, I forget, I think "Engineering to win" is a good reference point.
Personally, I have built many frames and repaired many others. Even some of the alloys from Europe respond well to the same theology as 4130.
John
PS, I use a portable band saw to cut material, if having to modify in the field a hacksaw is better than a torch.