I remember rebuild kits. ALLEGEDY, what you could do is sawzall your existing mag, buy a kit, rebuild it and call it a replacement for the old mag. Buy a $10 beater hi-cap AR mag that had no feed lips anymore and replace it with a brandy-new one. Ditto for a NFML/NDF Glock mag.
There is two sides to this (forget legality, but Len will surely reply and tell me if this was even legal, MA-wise):
1. You're never ever ever going to get "caught" with a post-ban hicap mag anyhow - WTF cares???
2. They're gonna nail you for something. Having a Vietnam era 20-rd mag cut in 2 isn't going to help b/c they are going to F you right in your B-hole.
Personally: I'm hoping 2-3 SC cases make all of these rules completely meaningless. Because there is no other way to solve this problem.
EDIT:
I was watching (rarely) 60Min about a decade ago. Maybe less. They were interviewing the Pope of the Orthodox Church. Back in the 60's, the Muslims pulled a similar Masshat move: They GO church requires the "Pope" to be trained (or born - I forget) in Turkey. Muslims took over teh country. Allowed the GO church to exist but closed the seminaries. Hence, after X years, no more Turkish GO candidates. Boom - GONE!
I found it rather interesting. Very long look on fixing your problem. We are 25 years since the original ban, right? How many mags gone? In the next 20, how many more??? The Democrats and the Muslims use the same playbook.