As for the warlock it would depend on what you want to get out of the melee aspect in AL.
For instance if the important bit is to be able to deal a great deal of damage in melee range you could add crossbow expert since it would allow you to use eldritch blast up close with no problems. In order to get that you would likely need to delay getting warcaster, drop warcaster, or drop an ASI. This would not help opportunity attacks though in slight compensation you would gain back three cantrips (you would replace the two weapon ones and shillelagh would no longer be needed) so there would be that.
Or if you really like the opportunity attack aspect and want to keep warcaster just where it is you could just use sacred flame. Yes the damage is not quite as high since you do not get the additional bonus damage from them moving like you would with booming blade but you do get your celestial damage bonus to it and it is still better damage on an opportunity attack than most classes get (3d8+cha mod is decent at level 12). Since it is a saving throw it would have no issues being used in melee range.
I think for AL the second option would provide the most bang for your buck and would be thematic to boot though it would be slightly less effective when used. Though remember that you do get three more cantrips that way and if you pick some fun ones you could be even more versatile than the original build while only losing a few dice of damage on the probably relatively rare opportunity attack (if the target does not move sacred flame does essentially the same damage as booming blade for you) for instance now you can pick up minor illusion how is that for versatility?
Personally I think it is still very effective sounding to me.