IMHO, not an easy move. The Learjet wing, while still retaining the multiple spars of its military ancestry, didn't have the structural provisions for underwing hardpoints. The structure could be modified, but it would be neither an easy nor quick fix. Now, some of the various operators have bought provisions for hardpoints built in new on their learjets (I think Finland did; I know they have an interesting ESM fit plus provisions for a centerline dual camera pod and for a starboard drop hatch). Retrofitting wing hardpoint provisions after the fact is quite do-able, but it's not done quickly, at least, not if you're concerned about airframe long-term integrity.
Oh, I should note that the Learjet wing is a single assembly from tip to tip that gets built up separately and then mated to the fuselage (much like the wing of the P-51). De-mating them is easy, but remating and re-doing all the electrical and fluid (fuel, hydraulics, bleed air for de-icing, etc.) connections takes rather longer.