I would like to do a rough cutting with a flat 1.5 mm bit, and do the last 1mm with a V carving bit. Is there a way to tell Luban to pause to change the bit?
You will need to create two separate toolpaths - the V-bit will need considerably different settings as the flat-end mill. Luban is limited in its ability to create ggod multi-toolpath-setups. You can “cheat” a bit with using the “allowance” value - refer to this post: Multi-Pass Rotary Guide - although it is for the rotary, the allowance bit should work for 3 axis also. Also, @Skreelink created a multi-pass guide for Fusion 360: Fusion 360 Guide For Multi-Pass 3D Engrave
Between two toolpaths you can easily switch bits.