Letter to Young Jimbo, Is Adding FSL/SSL Acceptable?

Just a quick question, as a fairly beginner lifter, 30 years old, ive found a Letter to young jim Template that appeals to me. Anyway for some added volume on the main lifts is adding a few sets of fsl or ssl acceptable for this program? cheers guys.

How long have you run the program as Wendler wrote it, and what were the results?