The legal documents are usually the least interesting part of a website, and in general I try to keep the numbers of legal documents to a minimum.
Nonetheless, there's no particular reason why not you cannot put the user content provisions in a separate comments policy document. However:
(i) users should be asked to give their express acceptance of the new policy (as well as the T&Cs);
(ii) you should amend the entire agreement clause in the T&Cs so that it references the new policy; and
(iii) you will need to renumber the document and change cross-references as appropriate.
Changing "your content" to "your comments" may be sensible where blog comments are the only user-generated content. However, if you introduce new user-generated content features in future then you may need to switch back to more generic wording.