SVN - Different client version on the same repository

I created repository with subversion client in version 1.6. Than I checked out the project with other client - with version 1.8.

Now when I want to commit changes - the 1.8 client ask me to do "svn upgrade".

If I will do "svn upgrade" to the working copy, and then I will commit some changes. Can I still use this repository with clients of version 1.6?

1. U wanna read at least ABC of SVN - SVN Book in order to split relevant and irrelevant data
2. U wanna to improve your memory - you got your WC with 1.6 client and access it later (still WC in 1.6 format) with 1.8 client (only such way you can see "please svn upgrade")
3. Version of WC doesn't affect in any way format of repository and accessibility of repository for client (while you'll use network-layer for access, not file-type): you can have in different locations different versions of WC for different version of client-side SVN with single any format of repository