This CS1.6 amxx plugin switches a player’s weapon hand via double-click on move buttons quickly.

change_hand.sma

#include <amxmodx>
#include <cstrike>
#include <engine>
#include <fakemeta>

#define PLUGIN "Change Hand"
#define AUTHOR "kingcc"
#define VERSION "1.0"

#define CVAR_CHANGE_HAND_TOGGLE_INTERVAL "change_hand_toggle_interval"

#define is_player(%1) (1 <= %1 <= max_players)

new max_players
new last_player_frames[64]

public plugin_init() {
    register_plugin(PLUGIN, VERSION, AUTHOR)

    register_cvar(CVAR_CHANGE_HAND_TOGGLE_INTERVAL, "24")

    max_players = get_maxplayers()
    for (new id = 0; id < max_players; id++) {
        last_player_frames[id] = 0
    }
}

public client_PreThink(id) {
    if (!is_player(id)) return
    if (!is_user_connected(id)) return
    if (!is_user_alive(id)) return

    new old_buttons = pev(id, pev_oldbuttons)
    new buttons = pev(id, pev_button)
    new status = get_cvar_num("cl_righthand")

    if (status == 1) {
        if (!(old_buttons & IN_MOVERIGHT) &&
            !(old_buttons & IN_MOVELEFT) &&
            buttons & IN_MOVERIGHT &&
            !(buttons & IN_MOVELEFT)) {
            if (last_player_frames[id] < get_cvar_num(CVAR_CHANGE_HAND_TOGGLE_INTERVAL)) {
                client_cmd(id, "cl_righthand 0")
            } else {
                last_player_frames[id] = 0
            }
        }
    } else {
        if (!(old_buttons & IN_MOVELEFT) &&
            !(old_buttons & IN_MOVERIGHT) &&
            buttons & IN_MOVELEFT &&
            !(buttons & IN_MOVERIGHT)) {
            if (last_player_frames[id] < get_cvar_num(CVAR_CHANGE_HAND_TOGGLE_INTERVAL)) {
                client_cmd(id, "cl_righthand 1")
            } else {
                last_player_frames[id] = 0
            }
        }
    }

    if (last_player_frames[id] < 255) {
        last_player_frames[id]++
    }

}