If I use the bolt shooter rule on a base of regraded legionaries (unskilled javelin, shoot and charge) does it shoot as artillery when they shoot and charge? (Assuming I charge at BW speed)

If I abandon the bolt shooter, does it become unskilled javelin, or no missile weapon?

Yes.
Unskilled Javelin.

Richard

If I shoot & charge and use the artillery to shoot, can I still abandon the artillery in the charge to get a full infantry move?

If a file has 2 normal legionaries in front, artillery in third rank, can it shoot with both javelin and artillery (in general, not specifically shoot and charge)?

No.
No.