Are Mak-90s considered pre-ban

Yes, a MAK-90 is considered Pre-ban if it is in factory configuration (either thumbhole stock or pre-89 pistol grip).

Does that mean you CAN'T legally swap out the thumb stock with a collapsable stock?

If you change the thumbhole stock out on a Norinco MAK-90 for a pistol grip/folding stock/etc., then Federal 922r applies.

The MAK-90 was imported into the USA after 1989.

Yes, NYS allows "pre-ban". I was looking to move there a couple of years ago. General rule of thumb: if you could have it during the Federal Ban, you can have it in NY. Prior to 1989, the Mak-90 was imported as the Norinco Type 56. After the 1989 Import Ban, they had thumbhole stocks put on them and were called, "MAK-90s". You can put the pistol grip and regular stock on it in NYS, provided you comply with federal 922(r) law. You cannot add a folding stock, because even though the weapon is pre-1994, none were ever imported in a configuration with a folding stock.

Check NYS Penal Law 265.00 definitions. Section 22 (e) v. says you had to possess them before a certain date.

Nick 007, The point of swapping the thumb stock is "I" don't like it. I purchased it a few years back for very little money despite that sucky stock and hoped to switch it over at some point.

Glad you like it... I don't.

A Dragonov stock fit the thumbhole intent. So does the Chote.

the Norinco MAK-90 was imported with the bunghole stock. if you remove the bunghole stock 922(r) applies and you must have the US parts count and probably (due to US parts count) need to only use US-manufactured mags to get to that parts count.