My current raster has positive values for all features but I need them all to be negative as it is for a seafloor basin. A handful of values are negative but most are positive. I have access to ArcGIS Pro.
Use the Conditional tool (either by itself or within Raster Calculator) to say "If value > 0 then multiply by -1; otherwise leave the original value alone". It should look something like this:
Con(raster > 0, raster*-1, raster)