stop processing further irules on condition match

You could use an iRule like this to detect if a prior iRule has changed the pool from the virtual server's default pool or issued an HTTP redirect (using HTTP::redirect) or response (using HTTP::respond):

when CLIENT_ACCEPTED priority 1 {
 
    Ensure this event runs first to save the VS's default pool name
   set default_pool [LB::server pool]
}
when HTTP_REQUEST priority 999 {
 
    Ensure this event runs after any iRules which should take precedence over this one
    Check if the currently selected pool has changed or an HTTP redirect/response has been triggered already.
   if { ([LB::server pool] ne $default_pool) or [catch {HTTP::payload replace 0 0 {}}] } {
      set already_responded 1
   } else {
      set already_responded 0
   }
 
   if {$already_responded == 0}{
 
       Do something like select a pool or redirect the client
   }
}

Or if you don't care about pool changes and just want to detect a redirect/respond, you could simplify the iRule:

when HTTP_REQUEST priority 999 {
 
    Ensure this event runs after any iRules which should take precedence over this one
    Check if an HTTP redirect/response has been triggered already.
   if { [catch {HTTP::payload replace 0 0 {}}] } {
      set already_responded 1
   } else {
      set already_responded 0
   }
 
   if {$already_responded == 0}{
 
       Do something like select a pool or redirect the client
   }
}

Both examples attempt to insert nothing in the request payload. If a redirect/response has already been sent in an iRule, catch traps a runtime error and a variable is set to track it.

Aaron