3. Some updates... if i understood you right this time, here's a 2- (or 3-) pronged approach to the problem
First, shift+alt+right drag will let you move both the global anchor, and *all* metasprites relative to it. This is effectively pretty much the same as dragging the entire canvas to see 'more' workspace without affecting the individual sprites' positions relative to the anchor. 
(edit: it doesn't seem like this gif attachment is playing back on my system.. so anyway, it was meant to showcase dragging both sprite, anchors, effectively the whole thing around the canvas without sprite x/y position readouts changing)
Secondly, i'm adding a "miscellaneous export settings" toolbox.
The reason is, after reading some discussion on nesdev, that some actually don't use signed 0,0 as their center position. This lets you set up an offset that only affects the generated text, not the workspace, which i think is what you requested initially. 
Thirdly, since these offsets make it more likely to run out of bounds (depending on what the specific engine requires; everyone makes different shortcuts and assumptions), you can set ranges for X and Y individually so the program warns and/or stops you if you're outside the desired value range with any of the metasprites exported.