グレイアウトのことでしょうか。
WS_DISABLEDスタイルを追加するかEnableWindowで無効化します。
#uselib "user32.dll"
#cfunc  GetWindowLong "GetWindowLongA" int, int
#func   SetWindowLong "SetWindowLongA" int, int, int
#func   EnableWindow  "EnableWindow"   int, int
#const WS_DISABLED 0x08000000
#const GWL_STYLE   -16
	button "ボタン1", *on_button
	id1 = stat
	button "ボタン2", *on_button
	id2 = stat
	btnwnd1 = objinfo(id1, 2)
	btnwnd2 = objinfo(id2, 2)
	style  = GetWindowLong(btnwnd1, GWL_STYLE)
	style |= WS_DISABLED
	SetWindowLong btnwnd1, GWL_STYLE, style
	stop
*on_button
	push = stat
	switch push
	case id1
		flg = 0
		swbreak
	case id2
		flg = 1
		swbreak
	swend
	EnableWindow btnwnd1, flg ^ 0
	EnableWindow btnwnd2, flg ^ 1
	stop