I was admitted to L&S for econ as a freshman, but i want to transfer to Computer science in the engineering school. Since I’ll have to take different courses to fulfil the requirements, is it allowed to transfer to Mathematics of Computation WITHIN L&S first (immediately before i start uni) and then in a year’s time apply for a transfer to computer science? Also, do I only have to take the minimum engineering courseload (1 math 1 science) and earn a gpa of 3.5+ in order to be able to apply ? cause the website faq says i need not have completed all prep courses when i apply, only the minimum, and that’s the minimum 
https://www.seasoasa.ucla.edu/ls-to-engineering/ describes changing to CS by those not in the engineering division.
If you just want to major in math (of computation or otherwise), see https://www.math.ucla.edu/ugrad/majors .