It looks like the function OnButton1() is the place where you are doing the resizing. You could either move modify the menu there, or return a status variable to indicate if the window is big or small.
For example:
CMenu* pMenu = GetMenu();
int isBig = OnButton1();
if(isBig)
{
pMenu->ModifyMenu( ID_STRICTION, 0, ID_STRICTION, "Striction" );
}
else
{
pMenu->ModifyMenu( ID_STRICTION, 0, ID_STRICTION, "Expansion" );
}