I'm sure the landlord said "no". Just a couple screws. Should have just changed it out and replaced it when you moved as suggested above.
The key words here are "Should have". Now that you went ahead and asked for permission and have been turned down, you may be on the landlord's radar for a surprise visit one day to make sure you are not messing with his electrical system and end up burning down his rental unit. I am not commenting on if it is better to ask permission or not (it probably is), just to realize that now you may be under scrutiny simply for asking, the world is funny that way sometimes.
Haha this is true, definitely on the radar now as questions on whether mining was even legal came up when they came to do some maintenance in the unit. An adapter seems to be my best option as I'd be looking to moving to a place that would allow me to modify the outlets.
I found this from AMAZON
https://www.amazon.com/NEMA-L14-30P-L6-30R-Plug-Adapter/dp/B004XWB2U8But even though it's NEMA 14-30 it doesnt match what my receptacle looks like... Am I missing something?