Wanting to add .wordpress.com to custom domain

Hello,

I apologize in advance if this question has a simple answer, but I haven’t turned up anything in the forum/web searches I’ve done.

I have a custom domain that I use with WP. I also have a separate account that is just a free wordpress.com account. I want to purchase a domain name for my .wordpress.com account through my current web host.

My question is, will I be able to simply change my login /email address for my free account, will I be able to add it to my custom domain account?

TIA