Yes!
Any latex paint can be added over the outdoor latex basecoat. I have used craft pearl paints to create beauty in the final top finish also.
All birdbaths have to get retouched yearly alas and alack to maintain the look...
Once all this has baked in the Sun for a week or so without rain,...they can be sprayed wit an enamel clear spray which will help you get through the year. All birdbaths have to be scrubbed out at some points from Spring to Summer with a dash of bleach and dried to keep them beautiful. Mine lapse sometimes.