You cannot change the charater to a w3d file.
Change_Character(obj,"c_ag_gdi_mp");
Should be:
Commands->Set_Model(obj, "c_ag_gdi_mp");
We don't know how you've set "Move" so we can't tell you is the teleport will actully work.
if(stristr(Msg2, "!<command>") == 0 && strcmp(Get_Player_Name_By_ID(ID), "<player name>") == 0)
{
if (stricmp(Get_Player_Name_By_ID(ID),"<nick>") == 0) {
Should be:
if(stristr(Msg2, "!<command>") == 0 && strcmp(Get_Player_Name_By_ID(ID), "<player name>") == 0)
{
After changing that you will need to remove a right brace "}" from the block.