I am currently a freshmen at Iowa State University and I currently have a 4.0 GPA and a 660 in math and a 510 in English for my SAT. I am studying aerospace engineering and I was wondering how hard it would be to be accepted at University of Texas for engineering (considering their acceptance rate for transfer students is so low). Would my SAT/ACT matter in my acceptance to UT or would it not (considering it is optional requirement to send a SAT score for transfer students) and how hard would it be to be accepted UT considering my grades at Iowa State?
idk what your chances are, but I would definitely NOT send your scores if you do not have to. If you do not send scores and they have to make their decision based on your excellent grades, you will have a much better chance imo. My son got into Cockrell last year (he’s class of 2020), but he did not get his 1st or 2nd choice major (ME/EE). He was an auto admit with a 1410 and 14 AP classes, and he got put into civil engineering. At UT it is exceptionally difficult to transfer majors even if you are already in engineering, so getting into a competitive engineering major like aerospace will depend on whether they have any spots and how many people are trying to transfer, etc. My son was told that if he went to UT and started in civil engineering, even with a 4.0 it would be difficult/unlikely to be able to transfer to ME. So, you have to consider that other engineering students already at UT are trying to transfer from something less desirable (civil/petroleum) to ME/EE or aerospace as well, and they have the advantage of being able to apply after their 1st semester, so spots get even more scarce for those transferring from other schools. I’m not saying it is impossible, but just be sure you have a back up plan or you are ok staying at Iowa. If you are trying to get to the state of Texas, I bet you could get into A&M, which is also a very good engineering school. My son got into several better engineering schools than UT (Illinois, Purdue), but UT is the ONLY school where he did not get his major. He is a freshman at the University of Michigan now. Go Blue 
Good Luck & Congratulations on doing so well in one of the hardest majors–my husband got his degree in aerospace engineering.
My high school graduation class has over 800 students, 64 of them scored full score 1600 in SAT. Our junior class is even stronger, this past August SAT alone there were 29 full scores. They literally haven’t started their 11th grade yet.
Past few years we had several SAT full scores with auto-admit could not get to BioMed Engineering or Electrical and Computer Engineering. Many of them opt out of UT and took full ride scholarship from other universities. Texas has over 3200 high schools so UT has to drive good students away because they cannot even take top 0.5% by the numbers.
I find it highly highly highly unlikely that UT would drive away auto-admit students who’ve scored a 1600. Some I can understand for the sake of balance, but a whole 3/4 of the auto admits at a school for a major? While I do believe that engineering is competitive, there are many other factors that come into play, such as essays and EC’s. Perhaps those students brushed off the UT app since it was a safety as an auto admit and focused on other schools that are more selective for OOS.
OP, apply and do your best on the application. Take everything said here with a grain of salt, since we are not AO’s or anything close to it. Try your best and see for yourself
Go for A&M and Purdue.