The procedure you think about should not be used in normal daily workflow with SVN because the repository history in Subversion is immutable. Instead of altering the existing revisions, you should commit new ones. I do not fully understand your case, but it seems to me that you want to start with a new release branch.
I cannot use branches in this case. But I could accept to change every version number that come after the extra commit
It should be very simple to create a branch and record those changes as a series of commits instead of a single one. This should be the easiest and the correct way.
PS You can use admin tools if you have full access to the repository on the server to perform a surgery on older revisions. However, this task is not trivial and may be harmful if you do not consider all the caveats. For example, what are you going to do with svn:mergeinfo after adding revisions in between existing ones?
r2000andr2001? Something liker2000½? Don't you just need to create a good old branch from an earlier revision?