I have several feature classes where I need to change the precision of a field from Precision 38, Scale 8 to Precision 18, Scale 2.
The field is of type double, and I tried to change the field with ArcCatalog emptying the table and it does not work.
Since you are talking precision and scale, I assume you are talking about enterprise geodatabase data? From Modifying field properties—ArcGIS Help | ArcGIS Desktop :
Some field properties can be changed after the table or feature class is created. For enterprise geodatabases, the properties that can be changed and how they can be changed depends on the database management system you are using; you can only make changes that your database allows. For example, if your database does not allow you to change the length of a field in a table that contains data, you cannot change the field length through ArcGIS.
What is the DBMS and what does that documentation say about altering precision and scale in-place?