You cannot use calculations in any of the GTRR parameters.
Closest approximation I can think of to get what you've requested would be to set up a series of GTRR steps inside If, ElseIf blocks of scripting.
Wham! Phil, that was quick!
A little too quick! I forgot that GTRR has a new window option and the window dimensions specified can be calculations--so there are a few parameters that can be calculations--but not the ones you've requested here.
You can pass key find and fieldname values as a variables or global fields
Go to layout by calculation
and perfom a find by using set field by name
To do the something very similar to GTRR
and if you structure it correctly you can make it very dynamic so you can reuse it most anywhere.
Sounds promising... I'll give it a try! Thanks