The center brace is load bearing. You will need to brace the tank if you remove that, even if temporary. <And it would be safer to drain down the tank, even part way while you are doing stand mod.> Perhaps a 2x4 frame with one leg inside the stand behind the sump, and a long enough 2x4 cross piece sticking out the front to give you room to work, then brace the cross piece to the floor with another 2x4. The problem is getting that back leg behind the sump, it may be impossible if you don't have some room on top of the sump.
Another possibility is to take it out the side (skinny way). If the side panel is easily removable, it would be simple to slide the sump out sideways. <Some DIY plans have removable side panel just for that.>
80 gal FW with 30 gal DIY wet/dry/sump.
9 fancy golds, 1 hillstream loaches, 1 rubber-lip pleco (C. thomasi), 3 SAEs, small school of white cloud minnows, planted.