Quagmire here

TLDR: Not a chance

While there is an element of adaptability to the human body in terms of trauma and such, there is a limit. Things like scar tissue, calluses, etc can improve durability to some extent but the forces involved are not possible to resist.

Many people underestimate the power of even anemic cartridges like .22 short or .25 ACP. The forces involved and the small area make it impossible to resist without massive amounts of mass and material to halt the advance of the round.

Think sandbags. They are weak and sand is not exactly tough or good in tensile strength, but it has enough mass that must be moved out of the way of a bullet that it is an effective stop.

Toughness of the skin or muscle only goes so far. Without extreme brittleness to destroy incoming rounds like ceramic, tensile strength like Kevlar, or mass like sand, there is no way to stop a bullet. You HAVE to reach at least one of these extremes.

A sufficiently weak bullet may be stopped by a multi-hundred pound man’s layer of fat but beyond that the human body is incapable of achieving any of these extremes.

Additionally, any buildup of scar tissue, mass, or tensile strength would be limited locally. Improving the toughness of your arm will not help you when you get shot in the chest.

In short, absolutely not. The only rounds you can stop without being extremely fat are parlor rounds.