As title says.
Yes you can.
How do I do that?
You can use: /cast [@mouseover, help] SPELL
That should let it cast on whatever you mouseover including yourself or you can use [@mouseover, help][@player] I believe which will cast it on a mouseover or on yourself if you don’t have anything hovering.
Those only work on my player portrait or in raid/party frames.
Could you try setting it up under blizzard mouseovers instead?
I already have that enabled and my macro has mouseover conditions, the problem is I can’t hover over my in game player, the actual troll in game that has my model, and have the spell mouseover cast on my model just like I do when I mouseover an enemy and cast a spell.
I seem to recall being able to mouseover myself in BFA, but maybe that’s just me, or maybe they removed that capability or it’s bugged.
Check the cast on self options? Ask in Macros forum, too? Maybe between both places, someone will have an answer. I know nothing about macros. So I’m useless except for those two suggestions. 
#showtooltip spell name
/cast [@mouseover,exists,help,nodead][@player] spell name
I don’t know about any way of being able to “self target” through your actual character model but any mouseover macro can and should be set up to cast on yourself if you aren’t currently mousing over another target.
I have mouseover as priority and want my bear form to cast frenzied regeneration if I have an enemy targeted with shift, wild bloom, rejuvination, regrowth, etc if mouseover on friendlies, and moonfire if just an enemy, and all the HOTs if no one is selected. Everything works except for mouse over my play character model which would make self casts much easier.
That’s a lot to ask of a macro lol. You’re going to need a better guru than I for that one. I tend to stick to single spell mouseovers and don’t really play around with that many modifiers in one macro.
I think it’s a blizz issue because I read a blue post somewhere saying they don’t let you select your character model intentionally, so that’s not good at all.
And like I said everything works great except for this issue on their part.
edit: I got it part way working if I use an enemy target as my mouseover que, but then it goes over my 255 character limit so it’s just double sad.
There was Super Duper Macro and Macro Toolkit, but not sure if they are still updated.