Justin Case wrote
I showed it to you already. A major modification requires supporting data
that is at the FAA's discretion.

Jesus Christ!

I guess so, thanks for being part of this conversation. Now can
anyone else add anything intelligent?

Yes. You may not like it, but he's right. The FAA (in the form of
your local FSDO maintenance inspector) is free to reject the data you
provide in support of your major alteration for any reason. After
you've spent some time performing major alterations on airplanes and
submitting paperwork for same, you will learn that the smart mechanic
finds out what the local FAA will accept (not what you think the law
requires them to accept) in advance. It's not good, it's not right,
it sure as hell doesn't improve safety, but that's the way it is.

Michael