Head mod??? What is it?

[PowerFiend]

Hi,
Newby to the KX5 world. I have been reading up on old posts and cam across a reference to many doing a head mod. What is it? Possibly resetting the squish clearance or recutting dome?

Also, I have seen that the KX5 can benefit from:
Stewart/JFab port cut in back of Wiseco piston.
PC P2 pipe
V-force 2 or 3 (one person referenced the KX250 v-force offering more midrange???)
Bolt from Stewart for KIPS.

Any of other bolt ons or simple mods that I'm missing?

Thanks.

[kaw rider]

readjust ignition timing & having head cut.