I ran in the bug RTE-bug here concerning TYPO3 7.6 and Chrome 73. I understand from here that I need to modify the rtehtmlarea/Resources/Public/JavaScript/HTMLArea/Editor/Editor.js of the HTMLArea extension.
Is there a way to override this file outside from the HTMLArea extension?
HTMLArea is a system extension and I am not allowed to change somthing in the typo3 source directory.
I downloaded the extension as a zip file from the TYPO3 instance but I cannot find the code which loads the JS in rtehtmlarea/Resources/Public/JavaScript/.
I tried to install the the current version for TYPO3 8.7 but did not work.
As you have downloaded the system extension you can upload it again as normal extension which gets higher priority then the system extension. Meanwhile all your uploaded extension will be normal extensions.
System extensions reside in ./typo3/sysext/ while normal extensions reside in ./typo3conf/ext
In this way you can modify the extension without changing the TYPO3 sources.