Passing Variables Between Pages

I want to create a page for adjusting instrument values e.g. enable/disable/min/max/alarm/trip values - potentially about 12 values for each instrument, I have about a 100 instruments. The screen is accessed by pressing the appropriate button on a P&ID style overview page(s).

I've done this previously using Allen Bradley with a single template style screen and then passing tag data via parameter files (there's other ways of doing it but that's another issue). I thought I would be able to do something similar with ABB using variables but for some reason can't seem to write to variables. I've used the obvious action - WriteTag but it seems to do nothing. I've tried adding a tag in the tag editor or using the variables widget. Neither works. So how do you write to internal tags/variables if it's not the WriteTag action? The SetBit action seems to work for booleans but I can't write to numeric or string values.

I'm an ABB PanelBuilder novice who should have done training but unfortunately got dropped in it and needs to get a panel working in a few days, no time for a course... I'm sure we've all been in similar situations!

If this doesn't work I'll have to create a table for all instruments but it's not a great solution. I'd rather have a page for each but not have to create 100 specific pages for each instrument.

NB: Only on simulator at the moment, if this makes any difference..