ntswift, refrigerant in a refrigeration or air conditioning system NEVER but NEVER "wears" out. It can certainly combine with contaninents such as water to form destructive acids but as long as it stays clean it never "wears" out. As long as no leaks occur or it gets contaminated the refrigerant will last forever and ever and ever.
You are absolutely correct about the importance of the vacuum process with a certain caveat. Minute leaks can occur in any refrigeration system. Sometimes the leaks are so small that only the larger molecules the gas can escape and the smaller ones are left confined in the closed loop system and maintaining a positive pressure. In that case you could certainly and safely recharge a system without vacuuming the system.
Digressing again, this is a complicated subject with thousands of "what if's". I can talk forever on this ubject.
Angelscrx, the short answer is yes absolutely you could do it - depending on your level of mechanical expertise and willingness to invest in a few tools. If I were in your situation I would do it myself but I've had a few decades of experience do this stuff. PM me if you're interested and I can walk you through it.
7 month old 100 gallon. Hopefully on my way to a great reef tank. A few small fish and a few small soft corals. T5 HO Lights and ro/di unit.