Here is a way:

Add an extra staff to the document.

Copy the chord symbols to this extra staff.

Clear the chord symbols from the original staff.

In the extra staff, move the chord symbols vertically back to the position on the original staff.

Now you can resize the chord symbols by resizing the extra staff.

Since you do not need the extra staff to display anything, de-select the staff’s display of everything: clefs, key signatures, time signatures, staff-lines, &c.

You can get rid of the staff’s barlines by moving the barlines vertically into the original staff.