Yes you can, however only as of AIMMS 4.73 when we introduced an upgraded Map Widget. You have to do this via annotations (CSS style). For details, see https://documentation.aimms.com/webui/map-widget.html#custom-tooltips-and-annotations-for-arcs

This version of the Map Widget has many extra benefits such as Maximum Relative Size for Nodes, Icons for Nodes, Store Focus with hover and select for arcs, Heatmap and Custom HTML Tooltips for nodes and arcs, Right Mouse click menu options and more.

As you can imagine, I do recommend upgrading to the latest version of AIMMS as that gives you a lot of extras and allows you to get the most out of AIMMS (4.74 is most current version).