The SetLuaFloaterValue() is useless, and improperly sets the root directory to a non-root folder (missing '|' prefix); it just fails silently.
The title of the floater is not changed when you change the value for one of its elements (here the inventory list root folder). Your "lua_inventoryAC.xml" floater definition is simply using a
title="Accessories" specifier in the
<floater ...> XML tag.
There is currently no Lua function to change the title of a Lua floater (I did not deem it necessary since, normally, Lua floater XUI definitions are designed for a specific purpose).