Profile field make not editable on edit and suggestion request

Hi,

I have one question and one suggestion request ....

question
How can make a non- ditable profile field when edit profile ? (same username field to explain better)

suggestion request
I would like to insert 2 custom fields (text fields) in profile that can be shown / editable one or the other depending on the selection of a boolean field , can give me some suggestion ?

Regards