It's a funny quirk in the ROC constitution - the constitution does not define the sovereign territory of ROC, however Chapter 1 Act 4 notes:
Presumably because it's not defined in the constitution, to define it would also require the resolution of the National Assembly. So who makes up the National Assembly?
Chapter 3, Act 26:
Naturally since the constitution was written in 1947 the starting assumption was that ROC would have control over mainland China, hence the requirement for Mongolian and Tibetan representation in the Natural Assembly.
Partly because of this, the ROC National Assembly was
until the "unification of the country". This power has passed onto Legislative Yuan. That said one could argue that without the (now impossible to form) National Assembly any changes to the constitution regarding territory of ROC is unconstitutional given lack of representation by nominal citizens of ROC (Tibet, Mongolia, rest of China etc) per the constitution.