Create a file in the startup folder, for me that's:
C:\Users\A\Games\Age of Empires 3 DE\76561198206085488\Startup\user.con
// Hotkeys to find units by tags
map("control-shift-b", "game", "uiFindAllOfType(\"AbstractHandInfantry\") ")
map("control-shift-5", "game", "uiFindAllOfType(\"AbstractHandCavalry\") ")
map("control-shift-6", "game", "uiFindAllOfType(\"AbstractLightCavalry\") ")
map("control-shift-7", "game", "uiFindAllOfType(\"AbstractRangedInfantry\") ")
// Hotkeys to select military gather points
map("a", "TownCenterAccel", "editMode(\"GatherPointMilitary\")uiSetProtoCursor(\"WaypointFlag\", false)")
map("a", "WonderAccel", "editMode(\"GatherPointMilitary\") uiSetProtoCursor(\"WaypointFlag\", false)")
map("a", "OutpostAccel", "editMode(\"GatherPointMilitary\") uiSetProtoCursor(\"WaypointFlag\", false)")
map("a", "TownCenterAccel", "editMode(\"GatherPointMilitary\") uiSetProtoCursor(\"WaypointFlag\", false)")
map("a", "TradingPostAccel", "editMode(\"GatherPointMilitary\") uiSetProtoCursor(\"WaypointFlag\", false)")
map("a", "DockAccel", "editMode(\"GatherPointMilitary\") uiSetProtoCursor(\"WaypointFlag\", false)")
map("a", "FortFrontierAccel", "editMode(\"GatherPointMilitary\") uiSetProtoCursor(\"WaypointFlag\", false)")
map("a", "BlockhouseAccel", "editMode(\"GatherPointMilitary\") uiSetProtoCursor(\"WaypointFlag\", false)")
map("a", "WarHutAccel", "editMode(\"GatherPointMilitary\") uiSetProtoCursor(\"WaypointFlag\", false)")
map("a", "NoblesHutAccel", "editMode(\"GatherPointMilitary\") uiSetProtoCursor(\"WaypointFlag\", false)")
map("a", "FirePitAccel", "editMode(\"GatherPointMilitary\") uiSetProtoCursor(\"WaypointFlag\", false)")