Thanks for the advice David.
Instead of topping up with water, I would be topping up with wort. How would I account for hops usage with this method? Any advice on how to manipulate Beersmith?
If I go with the partigyle method, I suppose I could take gravity measurements on the two batches and run beersmith on the fly to adjust hops in each.
After typing this, I realize my original goal is two have two kegs of the same beer which I was not clear on. By mixing the two, I will have the same but I just don't know how to make beersmith calculate it for me.
Thanks for the "beer for thought".