The original "Poor Man's Micron" is as follows. Replace the .3mm C tip from the HP-C, with a .2mm tip from the HP-B. Keep the needle the same
I also recommend replacing the standard separate trigger, and plunger system with a trigger from a HP-BC. It is not only a single piece, that feels smoother, and wears longer, but is taller, which is important for detail control. Especially since you have lost a bit of needle throw with the tip exchange. This taller trigger is where the idea for the taller trigger in the new Kustom Line came from. That is about all you have to do to create your poor man's Micron.