If maths is in the uni entry requirement for a course, then application of maths is not normally accepted as an alternative. Some STEM will expect higher maths at first sitting (S5)/you will be competing for a place with students that have this. It all depends on what type of course and uni, or college, you are aiming for.
Have you looked at the uni courses you are interested in and their entry requirements to see what subjects they ask for? If you are unsure you can email the university for advice.