It will I guess technically make it leaner but it is more of an advantage for atomizing the fuel, making it frothy. That frothed up fuel burns better than just straight fuel droplets.
Think like a progression. If that tube is solid, more or less straight up gas gets sucked up, fouling plugs from overrich conditions. Kinda like clogged emulsion tubes
Now the tube with holes (or cleaned up holes for that matter) allows air to get sucked in and mix with the fuel atomizing it. To a certain extent it is all good unless holes get uselessly large. It is technically leaning it with the pure fact that more air is paired with the gas but it is a good thing because it is a better quality "charge" that enters the chamber
I have done the emulsion tube mod to my bike and have had absolutely no issues with plug fouling. I have no baseline to compare to because I did my tubes before my bike ever ran in my possession. But except for a leanness at 1/8 to 1/4 throttle I'm fixing with stepped up pilot jets I have good tan plugs.
