During my analysis on a UPX packed binaries, I loaded it to LordPE and tried to study the difference of original and packed binaries.
After the UPX packed process, 4 chances has made to the PE format :
OEP - for sure this will change!
NumberofSections - The original binaries has 4 sections. But now it only contain UPX0,UPX1 and .rloc section only.