If a student desperately wants it to count then sure. But being realistic that is very rare especially for courses such as MX2 because the external tuition fees are way too much. Same with things like EX2.
I used to advocate external tuition for this stuff but when I found out how dear it was I was like ok stay away.
When you mean "external tuition" do you mean sitting the course out of school and it counting to the HSC, or do you mean "external tuition" in the sense that you are getting tutored for that subject in order to supplement your learning at school?
You do realise how popular MX2 is right? Especially at top 10 schools. A school like James Ruse has 96 spaces for MX2 equating to 4 classes (the rule is 24 per class for seniors) but at least 120 students in the cohort are interested in MX2 (with 150 students in a cohort from memory). In this case we have 24 students who have missed out on the course but are very capable and interested in the course (the school can't make another class due to a reason such as it will affect the timetabling system)
It may be expensive however if this is the one and only chance you can do the course for the HSC (and want it to count) then yes you're going to have to fork out a tonne of money in order to make it work. If you can't afford those fees, then get a part time job at say like Mcdonalds, KFC, etc that way you can pay for it without making your parents go through the burden of paying those fees