How to modify page rights with Velocity

Hello, I need to automatically set rights for a page with Velocity I have some ideas on the way to do this : get the list of rights already set for the page, check/modify them and eventually add more rights entries if necessary. The code will be something like : #set($rightindex=0) #set($rightsobjectslist=$doc.getObjects("XWiki.XWikiRights")) #foreach($rightsobject in $rightsobjectslist) current rights n°$rightindex are : groups=$rightsobject.groups ,users=$rightsobject.users , levels=$rightsobject.levels , allow=$rightsobject.allow; ##check if rights_0 exists and modify it #if ($rightindex==0) #set($userobject=$xwiki.getDocument("XWiki.aXWikiUser").getObject("XWiki.XWi kiUsers",0)) #set($rightsobject.users=$userobject.name) modified users for rights_0 = $rightsobject.users (...) #end ##check if rights_1 exists and modify it #if ($rightindex==1) (...) #end #set($rightindex=$rightindex+1) #end #if($rightsobjectslist.size==1) ## create missing rights #end $doc.saveDocument() My problem with this code is that the value of $rightsobject.users doesn't change ! It is "XWiki.XWikiGuest" before the #set($rightsobject.users=...) and it still is "XWiki.XWikiGuest" after ( instead of "XWiki.aXWikiUser" ) If somebody can help, it would be nice Thanks Yan