Can you take 2-25rd mags and produce a 50rd drum?
That would actually REDUCE the number of large capacity magazines that you own.
No law against that.
Also, it's never necessary to combine two mags.
Any mag that holds over 10 rounds is a large capacity mag.
There's no limit to how many rounds it can hold once it's a large capacity mag.
This is the same reasoning used with preban 1919 belts.
Don't EVER run them down below 11 rounds.
If you do, you forfit that belt's existence as a large capacity magazine.
What some beltfed shooters do is to put a blank/squib as the 12th or 13th round to make the gun stop.
Then, you can re-load that belt without it running below 11 rounds.