The freeze command line is:
svnadmin freeze repo command arg1 arg2 ...
To freeze multiple repositories an admin must chain these:
svnadmin freeze repo1 svnadmin freeze repo2 command arg1 arg2 ...
An easier to use interface would support both:
svnadmin freeze repo command arg1 arg2 ... # one repository
svnadmin freeze -F file command arg1 arg2 ... # one or more repositories
where file contains a list of repositories.
I suppose the iteration could happen in svnadmin or in svn_repos_freeze. Since
the API is new we should decide whether we want to change it before the 1.8 release.
Improvement
Major