Yup. In theory (and that´s pretty much "anytime I tried it"), you can simply paint over a well-dried enamel paintcoat with acrylic products. Only thing that might prove difficult, if you use a thin water solution (ie a wash or brush-on varnish), it might pearl off shiny enamel surfaces. But with dull enamels and spray varnish, there shouldn´t be too many problems.
Note that I´m a staunch "acrylicist". But I started out with Revell enamels, and they were rather good, indeed - but I just can´t bring myself to accept the disadvantages any more (stench, thinners, et al...).