Can you add unlimited data to Internet basic?

Trying to control cost in my household, so here is my question.

We currently have the 100Mbps Preferred with the 1TB cap, and I found myself constantly watching my data usage. 

I do not need out and out speed, Cox recently bumped me up 100Mbps but that will only make the situation worse, I will just reach the cap sooner!

So Cox, can I drop down to the Internet Basic (30Mbps) and then add on unlimited data?