Yes you can manually assign a net to an object. Please perform the following:
1. Select Object(s) that you wish to assign to a particular net.
2. Go to menu: Edit / Properties...
3. Select the net name you wish to assign to the selected objects.
4. Press OK.
Note: If you wish to create a completely new net, go to the Netlist Table... (menu: Tools / Nets / Netlist Table...), and select "Create Net".
You can also Merge and Delete nets.