[ZaX]

Im not sure if this is the best way, but it should work

#include <amxmodx>
#include <amxmisc>
#include <fakemeta>

#define TAG "MyTag"

new pCvarForceTag

public plugin_init()
{
    pCvarForceTag = register_cvar("amx_force_tag", "1");
}

public client_putinserver(id)
{
    if(is_user_admin(id))
    {
        set_task(2.0, "ForceNameChange", id);
    }
}

public client_infochanged(id)
{
    new szOldName[32], szNewName[32];
    get_user_info(id, "name", szNewName, charsmax(szNewName));
    get_user_name(id, szOldName, charsmax(szOldName));

    if(!equal(szNewName, szOldName))
    {
        if(is_user_admin(id))
        {
            set_task(2.0, "ForceNameChange", id);
        }
    }
}

public ForceNameChange(id)
{
    ForceTag(id);
}

public ForceTag(id)
{
    new szName[32]; get_user_name(id, szName, charsmax(szName));
    new szNewName[32];

    if( get_pcvar_num(pCvarForceTag) && (containi(szName, TAG) == -1))
    {
        formatex(szNewName, charsmax(szNewName), "%s %s", TAG, szName);
        set_user_info(id, "name", szNewName);
    }
}