When you change a list in a module (whether its at the module level, or for a single line item), any related formulas must be aligned with the dimensions... this could relate to formulas in the module you are changing, or formulas in other modules (or even lists) that reference the module/line item you are changing.
When I make these types of changes, I usually do the following:
Back up the model, or create a copy and perform these changes in a copy first.
Create a copy of the module you are changing.
Remove all the formulas from the copy (they exist in the original module, so you can restore them quickly)
Change the dimensions as needed (in the copy)
Restore the formulas... you many have to change some of them based on how you changed the dimensions
Link the new module into the model as needed, and then unhook the old module
Unit test to ensure that the replacement module is doing what its supposed to do
Assuming all is well, delete the old module
Rename the new module to be the name of the old module
This sounds like a lot, but its quite efficient and orderly.