In Numbers, how can I convert a number to negative.
E.g.
200
233
186
Becomes
-200
-233
-186
In Excel, you can use tools like Paste Special, but these don't exist in Numbers.
A workaround is to create a column with formulas like "=-1 * A1", then copy and "Paste Formula Results" (⇧⌘V). But I'm sure there are better solutions.
It would be awkward, might not be worth the time, but you would need to program this in automator using numbers hooks for automation / accessibility. That way you could make a service to swap the sign of whatever is selected.
Short term, you'd manually change each or set up a function to calculate the negative of the selection and then paste the values over the source.
This is one of the features that just isn't baked into Numbers (yet).