I've a question about weapon mods (if anyone cares to answer): will all the base firearms [energy, explosive and conventional] be customizable with any weapon mod? Ex. lever-action rifles with laser sights and scopes, magnums with silencers, etc. Or will weapons be confined to using specific mods?
The mods you buy or find will enter your inventory as a specific item, ie:.
357 Magnum Revolver HD Cylinder. This is one condfirmed mod for the .357. As far as I konw, Josh has said there is a tab in the GECK where you can define up to 3 mods for each weapon. It seems the mods you select come from a pool of available mods that have fixed effects, so the extended mag mods all probably add an additional X% ammo, the accuracy mods decrease spread by X ammount, and so on. If you're on PC, you could fire up the GECK and change the mods to whatever you want from the available list, but console users will be stuck with the ones Josh has defined in the core game.
So to answer you question directly: No. Weapons will only have 3 predefined mods available and distict to that weapon. They will show up in inventory as above, labeled for that weapon. I believe tha pip-boy interface to add a mod will be much like the repair or ammo type menus,where only the available mods for the weapon equipped will be selectable.