I was waiting for that excellent question to come up.
I thought about adding a word about it in my post, but thought better of it in case it turned into information overload. lol
To answer your question, yes, I do use different concentrations at different times depending on things, and that's where the beauty of master-batching with a 50% lye concentration comes into play. With a 50% master-batched lye concentration it's super easy to do the math it takes to adjust the master-batch solution to match whatever different lye concentration I want to use in my soap batch. All it takes is about 15 seconds (if that) to perform a simple, 2-part elementary math equation, and voila- I now know how much extra water I need to add to my batch.
Edited to add an earlier post on how I do the math:
https://www.soapmakingforum.com/threads/making-bulk-lye-for-multiple-batches.26634/#post-253997
IrishLass