you should probably post your questions to the products section, not the champions one. Unlike what one could think, you would be much more likely to get an answer. See Getting the most of the community when you have a Marketo question
Now, I do not really see a better way. There are 2 possibilities with regards to picklists:
- either you are looking into a field that is mapped with a CRM picklist field. In this case the list of possible values will the one from the CRM
- or you are looking at any other field. In this case, the list of possible value is extracted from the actual values in you DB
Marketo, unfortunately, does not provide the possibility to create picklist fields, only string fields. And whatever the possible values in the picklist, you can still post any other value to the field.