I fully realize that a lighter bullet with the same charge produces lower pressures, but that was my point. If the weight difference between the two bullets is significant, which 155 gr. to 124 gr. would certainly qualify, it could easily create a squib. And friction is going to be a bit greater with the 124 gr. plated bullet, compared to a lead bullet, so this could create a problem also. Think of it this way, would you use the same data for a 124 gr. bullet for a 155 gr. bullet?
And yes, as far as OAL, 9mm is one of the highest pressure and oal sensitive AL cartridges around. Speer #10 states that pressures more than doubled with a developed load producing a normal 28,000 cup, and jumped to 62,000 cup when the oal was deliberately reduced by only .030".
IMO, anytime you change a component, and especially one this significant, the load should be reworked. I don't have any experience with either the bullets or powder the OP is using, but it might not be a bad idea to locate some data that's relevant to the bullet weight, profile, and construction. Might save him the frustration of removing a stuck bullet from the barrel.
GS