but I was referering to the engineering side--not the end user
If I read your question correctly ...
(a) the takeoff calcs are for one set of runway data ... you can't make one bit BFL and another bit unbalanced, etc.
(b) nothing secret about the process .. for those aircraft whose AFM permits unbalancing, one just iterates the calculation with different levels of unbalancing until the RTOW for that given data set is maximised.
(c) this is constrained a bit if the output is graphical but, for the normal tabulated RTOW tables, it is a doddle and each point can be optimised without consideration of others .. at the end of the day the pilot needs the speed schedule and the unbalancing extent is buried within this output.
(d) there is no reason why the data cannot tell you the extent of unbalancing but that is not normally done
If I have missed your point, do try again and I shall endeavour to be a more diligent reader.
Mutt .. that's a tad cruel ....