As @TroyHunt posted, it is not possible to use SharpSVN to manage Subversion access rules. In fact, every Subversion+Apache server that uses mod_authz_svn can be configured to use a number of authorization lists. They can be per-repository authz files, authz files for the whole sever instance or even in-repo authz files (available beginning with Subversion 1.8). Therefore, there is no standard way for access rules management that will suit all Subversion installations. However, you can always write your own script specifically for your Subversion server installation just because Subversion authz files have a very simple format.
The original answer implies that you were using VisualSVN Server. In such case I have good news for you because VisualSVN Server 3.4 introduced a number of PowerShell cmdlets for server and repos administration. In the most recent 3.5 release, there are actually 29 cmdlets and cmdlets to manage access rules are among them:
For more information about the cmdlets and usage examples, please read the article KB88: VisualSVN Server PowerShell Cmdlet Reference.