Generally a valve job like that would cost more than avenger purchase price. While I think balance valve is great I'm not sure if you will see any major improvement on an Avenger because the Avenger valve is of a newer design and has no issue opening up and very efficient as long as you don't use too much hammer force. out of box the 25 cal avenger has no problem reaching well over 50 fpe which is mind bending for a $299 gun.
The juice ain't worth the squeeze if you ask me. Obviously if you have the skills and machineries to make a valve yourself and looking for a tinker project then we would love to see the results.