I too am frustrated by border thickness limitations with conditional formatting.

I have a sheet that is formatted to fit on an A4 sheet.
The text sizes are all defined to make it easy to read
I have two predefined border sizes on the sheet
Thick for major section division
Thin for sections within the major section
The border color is Red regardless of thickness
There are cells that do not have borders
I have a need to change all existing border colors to Green when a cell has a particular value in it.

When I use conditional formatting, I only want to change the color not anything else but it always changes the existing thick lines to thin. This completely mucks up the layout because the row height and column width changes when the thick borders are changed to thin.

Is there any way at all to create a rule, or formula, or anything, that only changes the existing border color and nothing else?