Instead of cluttering up the description with the ConVars, I'll just put them all here.
You either need to be in singleplayer to use these, or access to a dedicated server's console if you're using it in multiplayer.

Server-Only ConVars

Name: npc_siamesecat_movespeed
Description: Movespeed of the cat, you'll get funny results if you put it up too high.
Default: 50

Name: npc_siamesecat_soundvolume
Description: Effects the volume of the cat's sounds, should be between 0 and 1.
Default: 1

Name: npc_siamesecat_hungerrate
Description: The interval of seconds inbetween each hunger tick, which means the period when your hunger bar decreases.
Default: 120

Name: npc_siamesecat_enabledeath
Description: Setting this to zero disables death completely, the cat will not die from starving, dehydration, or weapons.
Default: 1

Name: npc_siamesecat_maxage
Description: The maximum age the cat can reach, the higher the age, the bigger the cat will become, the cat will also die eventually at this age.
Default: 5

Name: npc_siamesecat_agerate
Description: The interval of seconds inbetween each age tick, this is when the cat gets older.
Default: 120

Name: npc_siamesecat_dehydraterate
Description: The interval of seconds inbetween each hydration tick, this is when the hydration decreases.
Default: 120

Name: npc_siamesecat_fatiguerate
Description: The interval of seconds inbetween each fatigue tick, meaning everytime this comes around the cat gains fatigue.
Default: 40

Name: npc_siamesecat_disablenavwarning
Description: Toggles the warning that displays to admins for 15 seconds when the map doesn't have a navmesh.
Default: 0

Client-Only ConVars:

Name: npc_siamesecat_enableparticles
Description: Whether or not the particles are enabled that the cats emit, such as a chicken bone when they're hungry. Setting this to zero will cease the particles.
Default: 1