Basically I had a mediocre time in high school and would prefer for my transcript not to be considered during the admittance process
If you’re a transfer, most colleges do not look at high school gpa as a factor of admission, assuming you have at least 30 community college units. I got accepted to USC, and was by no means an excellent student in high school.
What I’ve seen:
If you apply to transfer before you’ve completed about 30-45 semester units, most colleges will require your high school transcript.
If you apply after you have 30-45 semester units completed, most don’t need your high school transcript. They may not need your SAT/ACT score, either.
If you apply to the UC system, they will only consider your performance in college. There literally isn’t even a place on the transfer application to put down anything related to your high school academics (aside from which high school you graduated from). I have known many friends who made it to top schools like UC Berkeley and UCLA who were either mediocre or even very poor students back in high school.
Thank you! That is very helpful actually 
Santa Clara U wanted my daughter’s hs transcript during the admissions process and she had 30 transferable. I have no idea the outcome as she chose a UC and then just notified SCU to withdraw her application. It is nerve-wracking if they ask, but not much you can do.
For UCs and CSUs, high school stuff is not required for junior-level transfers (i.e. those who will have 60 credit units by the time they transfer, often meaning that they have completed about 30 with another 30 in progress in the academic year that they apply).
For lower division transfers with fewer credit units, UCs and CSUs do require high school stuff, but no UCs are currently accepting lower division transfers, and only a few CSUs are.
A couple “good” colleges I’ve come across only need “proof of high school graduation” if you’ve complete some college.
Thinking out of the box, I wonder if a letter confirming your graduation - certified by an official at your high school will suffice (if they’re willing to write one)…or even a copy of your HS diploma. Might be worth asking the university’s admission office if they’re willing to accept either (if all they need is proof of high school graduation).
The UCs.
I would not worry too much about high school transcripts to be honest. Many top universities will want to see them, but if you have proven yourself at the next level (one to two years of undergrad), you will be fine for admissions. I was very worried about it, so were many of my friends, but we ended up leveraging our poor performance in high school and said that we have revived our academic track record. Use it to your advantage and don’t let it hold you back.