Here's the story.
My saxophone ensemble is playing Ronde Des Princesses from the Firebird Suite.
I have a piano reduction of the rest of The Firebird Suite.
Can I legally study the piano music and rearrange the parts for my saxophone ensemble to perform it for something like a fundraising dinner?
Would this be arranging, transcribing, or plagiarism?
(I have experience with notation software and with arranging stuff to avoid voicing problems...Just want to know how "okay" this is.)