As you're in the USA, it's likely that you'll attend ITC tourneys, and the ITC has rules for this. Here's the link. Scroll down to page 7, "Administration, Hobby & Prize-Support Policies
Modeling and Painting"
https://docs.google.com/document/d/1bUs0HrJ3f6YzR6mWlT1LRLq0i9_0ekf7ah9WhCTxsIo/edit#heading=h.f1sopnrg6vkb
TOs generally follow those rules, as best I experience.
Spartan089 wrote:This particularly came up when I was thinking about up-scaling my old marines to Primaris proportions so I could use them as such, but would I even be allowed to use them as Primaris?
I haven't seen this tried (all through 8e) but I'd bet it'd be a no go. The model is bigger, taller, etc. *Maybe*, if I were the
TO, and I'd seen that you put your dudes on 32mm bases, and built up the base to give that teeny bit of height, then maybe it'd be acceptable; with Rule of Cool being a factor. If it's a half harted conversion then it might not fly.
As events are run by businesses selling
GW product, this is not likely to get much traction. I know the biggies,
BAO,
LVO & So Cal Open wouldn't accept them.
Spartan089 wrote:What about a Chaos player using
CSM with loyalist rules as long as his models abid by
WYSIWYG?
I pulled this off once. I wrote up a silly note/story that ChoasSM agents infiltrated a Space Wolf chapter as Long Fangs (with
MLs), and had to hurry back, join their regular traitor buddies, and didn't have time to change. I'm not a top table player and the kiddie pool gets rather casual. This was at 8e's beginning, but I don't think it'd be accepted again.
I checked in with the
TOs, got a smirk out of them and approval. It's entirely possible that I got away with it as most players in Calif know me, know that I'll likely go 1-2 or 2-3, and don't care what I put on the table. This was ... 3 years ago. Or 4.
Things in the ITC are tighter now.