What will be the style?

The princely families of Monaco and Liechtenstein are "serene highness" at least. But what will happen if an heir/heiress presumptive ascends to the throne who happens to be married to a prince, duke, etc with the style of either a royal, imperial, or both imperial and royal highness at the same time or a child of a deceased heir/heiress apparent/presumptive who were born as either royal/imperial/imperial & royal highness ascends the throne? Will the style of the newly ascended sovereign prince/princess be changed either to the style to whom she is married if it's higher than serene highness or to the style he/she is born to?