Well, the .p3d model files from the ArmA game are ODOL format, which means they are binarized.
Oxygen will not open these, Oxygen can only open MLOD format p3d model files.
So, no real way for you to edit ODOL files, however you may be able to retexture them by using a hex editor to change the texture names and the paths to new texture names and paths, however......with these ODOL format files the length of the new paths and texture names must be the same as the old paths and texture names i.e. if the path plus texture name came to 17 characters in total for a particular entry, the new path plus texture name must also be 17 characters for that entry.
Planck
Edit: Actually, this doesn't work most of the time, but some of the time it does, and i haven't worked out why...
ahh... not quite correct... all texture paths in odol v40 are Asciiz strings... which means they are 'null' terminated.
so you can have a different length texture path than the original.
eg. when hex editing the file if you were replacing the texture...
ca\tracked\data\m1abrams_mg_mount_co.paa.
= 41 (including the 0x00 after the .paa)
you could replace with...
aawTracked\m1a1\tx\mg_mount_co.paa.
= 35 (including the 0x00 after the .paa)
the thing you
have to do is
shift ALL bytes after the original length 0x00 (null) up the appropriate difference.
In this case 6 bytes.
If you use HexWorkshop it asks you automatically when you do a 'Find & Replace' if you want to do just that... dunno about other hex editors.