Due to surgery on my shoulder I have trouble keeping my arm up. Can I lean my arm on another Kohen’s shoulders by Birchas Kohanim?

If you wont fall if he moves away then it is permissible. You may also put your hand down between each word.

 

Sources:

משנ״ב קכח ס”ק נא-נב; ביאורים ומוספים דרשו, 69-70