I spent 30 years of my life in the Marine Corps, from 1986 to 2016.
The Marine Corps does not have "shorts".
Underwater Dive Trunks (UDTs) are worn by swimmers (i.e. divers, recon in boats, et al.) but not away from the water. Unlike SEALs who will wear them with a utility top, Marines simply do not do that.
By the way, SEALs would only do this in a work environment.
The shorts in the photo look nothing like any US uniform I know, and UDTs do not have a cargo pocket, and are really short. Like micro-short. Slightly more than speedos. I wouldn't wear them in the bush.
Uniforms are not modified "in garrison".
In the field (and I mean the real field, not just away from home), yes, uniforms get faded, torn, and otherwise blemished. This is fixed when returning to garrison.
I can't speak for Iraq, but no one had service uniforms in Afghanistan. So there wouldn't be wool trousers. And no service uniform (as opposed to dress or utility) would have cargo pockets. Only utility trousers have cargo pockets.
Field Grade Officers would not "modify". I don't know a Marine Corps General Officer who would modify. It is clear there is at least one person here who does not know the difference between a Field Grade Officer and a General Officer.
Keep in mind, Marines do not even wear utilities (i.e. camouflage uniforms) off base, except commuting directly to/from quarters. There are exceptions made for emergencies (i.e. assisting a stranded motorist), but not stopping for gas before leaving base or even going through the drive through. Does it happen? Yes. Do First Sergeants and Sergeants Major like correcting people who make such mistakes? They surely do.
Have I seen older camouflage trousers turned into cut-offs? Yes. But not on base, and not where there may be photographic evidence. Although, keep in mind, when a style becomes obsolete, it is no longer a uniform. The old woodland camouflage? Obsolete by MARPAT. Ditto the chocolate chips I wore in Somalia. They are no longer considered uniforms at all. Fun fact: when out of service the trousers can be worn, and the service jacket can be worn, but the buttons must be removed. That eagle and anchor means something.
"No part of a prescribed uniform, except those items not exclusively military in character, will be worn with civilian clothing.
(1) Items authorized for wear with civilian clothing by men are restricted to the gold cuff links, studs, necktie clasp, mourning band, footwear, socks, gloves, undergarments (the green undershirt may only be worn for PT), black bow-tie, green wool scarf, general purpose trunks, and crew neck-service sweater, the all-weather coat, tanker jacket, the dress blue sweater without insignia of grade (with or without epaulettes)
, cold weather physical training uniforms and Marine Corps running suits (see paragraph 2006 for wear guidance).
(2) Uniform items authorized for wear with civilian clothing by women are restricted to the white shirt without insignia of grade, footwear, gloves, green undershirt (for physical training only), handbag, clutch purse, mourning band, crew-neck service sweaters, green wool scarf, general purpose trunks, the all-weather coat, tanker jacket or the dress blue sweater without insignia of grade (with or without epaulettes), and cold weather physical training and Marine Corps running suits (see paragraph 2006 for wear guidance).
(3) Uniform items that have been declared obsolete may be worn with civilian clothing, when appropriate, provided such items contain no distinctive insignia or buttons."
It's all spelled out pretty clearly in MCO 1020.34H. I don't know why this is even being discussed. The references are readily available.
