Your dreamself reflects who you are; Vriska got a new arm and eye because she wanted it, but Terezi stayed blind because she was happier that way. But what if someone changed their mind? For example, if somewhere along the way Terezi decides she didn't want to be blind anymore. Would their dreamself change to reflect that? Or is that not possible?

As long as their dreamself isn’t their mainself they can change it as much as they like. (See Jade growing and ungrowing multiple limbs)