Never set an item quantity above 99 unless the item naturally stacks to 99 (e.g., potions stack to 10, but monster parts stack to 99). Setting a Potion to 99 is fine; setting a Plate to 999 might soft-lock your game when you try to combine items.
Based on analysis of the two most cited editors (version 2.0+ of the ＠kusumik editor, last updated ~2014–2015): monster hunter portable 3rd save editor
A: Yes. The best editors let you give your Palico skills they cannot normally learn together (e.g., Shock Trap + Barrel Bombay + Piercing Boomerang). This is considered "legal" because Palicoes can learn any skill through the inheritance system, albeit rarely. Monster Hunter Portable 3rd Save Editor — Complete
Using save editors requires care: always back up original saves, use trusted community tools (prefer open-source or well-reviewed releases), and avoid using edited saves in multiplayer contexts where it could harm other players’ experiences. A: Yes
Create "God Charms" by assigning specific skill values or unlock every weapon and armor set in the game.
Add high-rank materials like Rathalos Rubies or Zinogre Jaspers without repetitive hunts.