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