What is the impact of changing the UDF Value Type

The UDF Data is not deleted when the UDF Value Type is changed but that data may not display unless the item is changed back to its original state.

This is because some data types are displayable - for example, a number can be displayed as text. 1,0 or "1.0" can be displayed as text, however, all text cannot be displayed as numbers. "1.0" can be displayed as 1.0, but "abc" cannot be displayed as a number.

Similarly, a number cannot be displayed as a date, but the date can be displayed as text, and sometimes text can be displayed as a date if the text is in a valid date format.

The bottom line is that IMPOWR preserves data, but it is impossible to show it in all cases. Users setting up UDFs and changing their Value Types need to do it in a responsible way.