At first I thought that the max was two commands but I input two long commands and it didn't work.
By the looks of it, its the number of characters and not the commands.
I dont know if its the source engine's limitations or the trainer's(the one I'm using).
I do know that:
ai_reaction_delay_idle 0 ; ai_reaction_delay_alert 0
cc_change_figure_height 2 ; cc_change_figure_bust 2
works and only the first command works for:
player_monster_damage_base_constant 3000 ; plr_move_speed_normal 1000
I guess removing the spaces gives you more characters to squeeze in.