Carpenter here. If landlord doesn’t have an issue with a large aquarium..I don’t think they'd have and issue with allowing you to remove and replacing the door frame.
Carefully score the caulking where the casing meets the wall to prevent wall damage..and remove replace the door frame. Worst case scenario if the frame doesn’t come out well. Can replace with a new pre-hung door. That’s what I’d be trying as that steel stand is pretty nice. Grinding, then welding indoors then repainting.. would be more headache imo.
The biggest issue that I have seen since measuring is that its not just the trim I will need to remove, it is also the door jam itself because I need that much more clearance. with the jam, it measures 29.5" I need 31" to fit the stand thru. The trim is one thing, but the door jam as well, seems like an entire reno.