If you want to change the name of a field of a message, you can use rename() rewrite rules. This can be also achieved via using set() and unset() but those require extra conditions and two operation instead of one.
The rename() rewrite rule uses positional arguments and they are both required. It supports condition rewrite. For more information, see Conditional rewrites.
Declaration
rewrite r_rewrite_rename {
rename("<string1>" "<string2>");
};
Example usage for the rename() rewrite function
The following example renames the .app.name into .container if the .app.name exists. Otherwise, it does nothing.
rewrite r_rewrite_rename {
rename(".app.name" ".container");
};