How to create custom fields that can be later mapped and used with "Convert" functions

Hello everyone!
I have set up custom fields and don't know if I am doing things correctly. My goal is to populate these fields in MP3Tag and hopefully be able to map them to new fields that may come to itunes or others in the future. That way I can enter the data now and just map the fields in on swoop later.

The way I have done this is by going to the Columns and creating a new column through "Customize Columns". I set up the name, eg "Genre2" and assign %genre2% to the value and the field.

I can also do this with the tag panel. I must be doing something wrong, because when I try to use the "Convert" tool "tag>Tag" the fields don't show up. I know I must have done it a different way because I do see a genre 7 in the extended fields, but no genre2, genre3 and so forth. I have tried to read on this but cannot figure out what I did differently with "genre 7" other than it has a space in its name instead of "genre7".

If someone can explain to me how to do this properly or point me to a link I may have missed while searching here. I would sincerely appreciate it.

Thanks!

If you want to add more than just one field of the typoe GENRE (or in fact any other type of field) you can use the extended tags dialogue and simply add another field of already used ones.
Like that you do not have to separate them to user-defined fields.

User-defined fields get added to the list, after you have entered them manually at least once.

Thanks ohrenkiko. I will try to figure out how to use extended tags. I will also check if I can get them new fields to show up by manually entering them, though I have not had much success. What do you mean by manually entering them? Do I do it in the tag panel or in a column?

The field selection list sometimes shows only the MP3tag standard fields. If you have user-defined fields then you have to type in the name as you cannot select the name from the list.
You can enter the field name as well in the tag panel definition and the column definition.