Hello Aspirant,

See for class 10th registration process was already conducted in class 9th once and in class 10th also it is conducted which is called as final registration for class 10th examinations but if you have already opted for Standard Mathematics then now you cannot change it to basic Mathematics and also if you want to opt for PCM in class 11th and 12th then you should mandatorily pass class 10th with Standard Mathematics otherwise you can only pursue streams other than that of Science (Mathematics) like Commerce,  Arts and so on.

I hope this information helps you.

Good Luck!!