Yes you can specify the weight as forces, but ...

1) You then need to insure that you put "F1" in every load case that also includes "W" or "WNC".

2) If the model is ever analyzed dynamically, the forces won't be considered, because they will be assumed to be "loads". Therefore this weight will have to be accounted for using the "Lumped Mass" option.

In my opinion, it is much safer and easier to include the weight as "rigid elements".