Naomi,
>You can open the frx with USE, and alter the fields. I do not know the fieldnames without searching, but you can REPLACE the code as well as the binary fields. Possibly from a template hidden into your program.
FWIW, this is exactly how we prepared ad hoc customer reports for years. Customers could select any combination of fields and the proc set up the report from scratch including set relation for lookups and addition of branding detail under our control. Even if the customer has or needs to use MODI REPO there's no reason why you can't go in and massage the report. Common uses include removing some fields in a demo version, ensuring that your company brand info stays intact, adding disclaimers if confidential fields are included, adding report variables, ensuring set relation for certain fields... Certainly worth considering, especially if you allow users to potentially screw things up completely via MODI REPO. ;-)
I know this doesn't answer your specific question- but you can cause a report to call a routine before it starts processing. That would be a good place to pre-populate calculated fields that don't exist early enough.
"... They ne'er cared for us
yet: suffer us to famish, and their store-houses
crammed with grain; make edicts for usury, to
support usurers; repeal daily any wholesome act
established against the rich, and provide more
piercing statutes daily, to chain up and restrain
the poor. If the wars eat us not up, they will; and
there's all the love they bear us."
-- Shakespeare: Coriolanus, Act 1, scene 1