after markets parts ?

Depending on how accurate the model is to the actual subject and what parts you're trying to use. Manufacturers do things differently, I have had some luck using common parts (seats, instrument panels, face plates) from PE sets, but the more specific (items that require removal of details) don't work well at all.

I was able to use the flap set for a AM Dautless and use it on a Hasegawa one, but it did take a whole lot of extra work since the Hase wasn't designed with the flaps extended. If you're going to mix and match parts, be prepard to do a lot of work and understand that not everything will just 'drop in'. 

As stated, sometimes the PE parts are rather generic and can be used on like models from different manufacturers. Other times, the PE set for that particular brand of kit will only work on that kit and not on another.

For instance, the old Verlinden PE/resin update set for the Academy M1A1 had about a 90% compatibility rate when using the set on the Tamiya kit. This is because that particular kit was heavily based on the Tamiya kit. However, the set had about a 50% compatibility rate with the DML Abrams kits.