Yes, a paid developer account or a DreamSpark (student account, free) will increase this limit, but only a little bit. It's intended as an anti-piracy measure. On WP7, it was a real drag because you needed homebrew (even without interop-unlock) to do some very reasonable, standard things. On WP8, those things are mostly possible officially now, and therefore you probably only need to sideload a lot of apps if you're working with high-privilege apps, and in order to sideload high-privilege apps at all, you must be interop-unlocked (which is, literally, the ability to sideload over 300 apps at once).
Win8/Windows RT projects:
List of desktop apps for hacked RT devices
Native Access WebServer and Libraries
WP8 Interop Unlocks
Storage Cleanup tool
XapHandler, Root Webserver, OEM Marketplace XAPs, Bookmarklets collection (Find On Page), Interop-unlock hacks.
Do not private message me with questions that should have been posted on the forum!
Not only are you wasting your time - I'm not going to bother writing an answer to such a question for only one person - but I will probably block you from PMing me in the future as well.