Will a new Modem force my ISP to give new subnet IP?

[dcyphure]

If i got a new cable modem, i'd have to call comcast isp and tell them i have a new one. Would they assign me a completely new IP..subnet and all?
This would circumvent any kind of forum ban right?

i know i could call and ask for new subnet but they ask alot of questions and then never seem to understand anything technical, they give new IP but same subnet cause i dunno, they dont get it i guess nor am i going to say its to avoid a re-ban ...plus my modem is very old and sometimes cuts out but it is not comcasts modem, i got my own when i first got internet from them, so i'm not required to use theirs or anything.

main reason being aside from old modem that cuts out sometimes.. over a year ago, i got banned from a forum cause i decided after a couple years of using that forum that i didnt like the funky name i had and stupidly i made a new one, against forum rules apparantly.
i changed IP, email...etc. but after a couple posts they find me out and ban me again. how i dunno, i assume subnet since its always the same.

i asked admin about it and apologized for new name but then they ban me from even viewing anything at the site. got tired of making new emails,names..etc. i even change my passwords, it only works temporarily then i'm IP banned, and somehow asking questions gets me a harder ban.

could stand a new modem anyway, i'll just tell ISP it crapped out but not sure if i'll get new subnet ip or not