Lol trust me its not fun you get bored of hosting soon but back on topic yes with a 3.55 you can put mw2,cod4,cod5 what ever hacks you want on and data transfer to your 4.20/4.21 ps3 and host and enjoy. You need 2 ps3s to host

Yeah, if your ps3 was on 3.55 with a patch then updated to 4.20, done 1 ps3 with a patch.

Yes.

1. If your ps3 is currently on 3.55 you can load the patches, then stupidly update your console to 4.21 and get online

Or

2. Buy a NOR flasher (if your console came with 3.55 or below from the factory) like ProgSkeet, E3, or teensy and downgrade it, put cfw on, load patches and upgrade to ofw so you can go online.

if you have only one PS3 on 3.55 or 3.41 and you dont want to update them then no, you cannot. if you had 4.20 then you could just use a spoofer to get online, but for 4.21 there is not one out yet. if you really wanted to host, then you could upload all of your patches to the 3.55 and update to 4.21. or if you had two PS3s then you can just do a data transfer from the modded 3.55 cfw PS3 to the 4.21 ofw PS3. hope i helped!