[Dr Big Bird PhD]

I went to my LGS to get some railguards for my AR yesterday and the sales person asked me if I had my firearm registered with the NFA. I obviously said
"no". I use a bullet button and use 10 round magazines, just like Big Brother told me to. He then pulled out a print out of the new legislation that will most likely pass the state congress.

To make a long story short Cali is going amend their AWB law to include fixed magazines. The SKS and AR/AK clones with bullet buttons will become illegal. However people such as myself would get a grace period to register my firearm as an NFA weapon. However He told me that I will no longer have to have a bullet button can use legally obtained Hi-Cap mags once its registered.

Since I'm gonna have to fill out all that paper work anyway, I figured I would do some research to see what exactly I CAN and CANNOT do before and after its registered.

-If registered as an NFA firearm, can I legally own another upper receiver in 6.8 or 300 BO? Or is the caliber and upper registered as well and I am limited?
-Once the law is passed and I am allowed the grace period, could I SBR or suppress the weapon since I'm going to pay the tax stamp anyway?
-If I wanted to change my stock or flash hider in the future, would the NFA registration conflict with my ability to alter the cosmetics or attachments?
-Since I will be able to use hi-cap mags, is there any legal way for me to obtain them or are they registered as well?
-Is there any other general advice or knowledge I should be aware of with NFA weapons?