I have taken 5 different SAT II tests.
I am content with all of my subject test scores except one (US History… RIP).
I plan on applying to at least one “all score” college… do I have to self-report this subject test score? I know I will have to send them all in, so the issue there would be my self-report not matching up with my official score reports.
The policy on each college’s website is rather unclear when it comes to self-reporting subject tests. I just don’t want other score-choice schools to see ALL of my scores if it’s unnecessary.
Thanks in advance for any clarification 
You CAN change the testing page (and any other page) before/after you submit to that school.
Just take care to stay organized if you decide to make changes between submissions to different schools.
Thank you for the clarification!! That is good to know. Does the same apply for the essays? I read something about the essays allowing 3 edits total in between submissions, but I cannot seem o find anything about it on the official CA website.
You can change the essay every time if you want (although I really do not recommend that).
https://appsupport.commonapp.org/link/portal/33011/33013/Article/2696/Is-there-a-limit-to-the-number-of-edits-I-can-make-to-my-personal-essay-once-I-ve-submitted-an-application
“Beginning with the 2015-2016 application, you are allowed unlimited edits to the essay after your first application submission.”