I just installed InDesign without Arabic support enabled, which I need, do I have to uninstall and reinstall it with that option on, or is there a way to do it without the uninstall/reinstall process?
You don't need to unistall the previous version. Read the following post
I suppose there are two methods.
Give it a go, hopefully one of these tricks will work.
I just tried installing the middle eastern version on my MAC which already has the English version installed(the latest version my MAC supports). I was not prompted for unistallation of the current version so probably the tricks won't be necessary i think. Try it to know what it exactly does is all I can say now. And also please do share your findings here so that the other person with this question is benefitted with your experience.
Correct Manan, no need to uninstall existing InDesign. To add another InDesign copy with Middle Eastern capabilities, just change the language in the Creative Cloud desktop application to "English يدعم العربية" then download another copy with a different version number.