It looks like there's a version, yes:
https://inkscape.org/en/download/mac-os/
To replace colors from the Extensions menu -> Color -> Replace Color. Just enter the hex codes of the color you want to replace with the color you want to change it to. When you're done, there's an "Export PNG Image" option from the File menu. You set the image size when you export, because it doesn't matter what the size is in the SVG file (that's one of the key things about vector graphics).
I wouldn't recommend exporting 150x150 PNG files, as Inkscape might stretch things to make it fit that size. Just export so that the longest side is 150 pixels and then use another image editor to pad the image out to 150x150 if necessary.
Of course, the menus might be a bit different in the Mac version.