An easy way would be to use the <Edit> <Select All> route but it sounds like you will have to be more specific than this.
Only way I know is to work through each form, highlight all the textboxes (using shift key and mouse click) and then making changes.
Its boring and tedious but it does the job.
There may be some fancy code you could use and if anyone knows it I would love to have a look too!!!
All best wishes
Solve one problem and create another!!!