Simply put. Can I attach a 10round mag permanently (make mag release permanently inoperable)  and be ok?

https://crossarmory.com/product/ar-fixed-mag-quick-pins-top-loading-kit-for-ar-15/#configuration

I'm assuming on an AR?  Not a lawyer, but its still an ar, still semi auto, but does it have an adj stock, flash hider, barrel shroud or pistol grip?

Also not a lawyer and my opinion is that this will not absolve you from having to submit a disclosure affidavit.

VooDoo

IANAL, but I would think so.

I'm also of the opinion that one is OK by removing the gas block/tube, and replacing it with a gas block (no tube) that is backwards, thus making it a straight pull weapon.  
You must either destroy, or send the original gas tubes out of state.

Either way, it is your call on what you want to risk.

The reason I ask is “ability to accept a detachable magazine”… permanent 10 round mag.  No longer able to accept a detachable magazine. Asking because it’s worked in New York and California

I guess it depends on if one thinks that this permanent Magazine/the firearm in question can yet be "readily modified" to accept a detachable magazine. I don't know enough about the modification kit but I'm pretty sure if it can be easily installed, it could be readily uninstalled and the firearm returned to it's normal functionality. The only way to really know is to do it and see what happens - The rules of this Game are so convoluted and contradictory that very little of it is plain to understand.

What is the ATF's definition of Readily Modified? Isn't it like 8 hours in a machine shop to perform the modification? Meaning that unless it takes a fully equipped machine shop 8 hours to do it is "readily modified". I'm just guessing....Illinois PICA is *not* California or New York.

VooDoo

I know the one kit has a plug you tap in with a hammer. I was thinking of going one step further and throwing a couple tig spots on it .

Well, from me best of luck to ya whatever you decide. This whole mess is an abomination.

VooDoo