Hi,
I have renamed the "Power" field to "Color"
Do you mean "renamed for viewing" or did you really change i_power field name in the table t_item_car_attr? If you did the latter remember you have to change also any possible reference to i_power in the plugin scripts.
Anyway, you can do this:
ALTER TABLE /*TABLE_PREFIX*/t_item_car_attr MODIFY i_mileage VARCHAR(255);
One line per field, using real field name (i_mileage, i_year, i_engine_size...). If you keep the names like this I think you shouldn't need to change anything in the scripts.
Build the list in a text file, save as "changes.sql" and use "Tools / Import data" in Admin Dashboard to download it and make the changes to your database. (Better do first a complete backup of the DB, just in case).
Regards