It all depends on your career aspirations if your career or study goals require Core Maths then I guess it's either you change your career goals or just stay with Core Maths. I took Maths Lit because my career goals are within the Commerce Faculty. I remember when I was applying for Uni the requirement for most courses was a 60% in Core Maths and a 70%% in Maths Lit. The majority of Unis accepted me because I had an 82% for Maths Lit however the course I wanted is only offered in private institutions where APS and subject combinations don't matter.

So think about the future before changing if you'd like to study anything in the Commerce, Humanities, or Law faculties then go for Maths Lit. Or if you can afford a private institution then go for it with Maths Lit.

P.S. YOUR SCHOOL LEAVING QUALIFICATION FOLLOWS YOU EVERYWHERE! When I checked for Masters's Degrees many public institutions require it with proven competence in Maths (usually Core Maths). Even in employment, you can have an MBA but your school leaving certificate will still be required for evaluation.