Currently when we customize member database field, let's say I add "Country" as one field, and I define the type as "text", which means that subcribers can enter their country name as a text, but if I want to change the type setting to other options, such as "multiple choice" or "dropdown" or "radio button", I can't change it. I can only delete the "country" and add a new field with a new type.

Can we change the database field type without deleting it, since we will lose the old members' info on that field.

You are right, at the moment field type can not be changed. I will make a note for our list of enhancements.

What you can do is create a new field, enter the values manually (which is a pain...), export the list, copy the whole column from old field to new and import back.

I should like some flexibility to be able to change field types for existing database fields.

For example I have fields which are current defined as text.  However members give different responses to the question in terms of capitalisation, abbreviations etc which make the behaviour of the search on data in that field erractic.

I'd like to be able to change such a text field to a picklist.

The database would still store a text value but the choice available to new members would be restricted by the list.  Existing membership records would continue to hold the existing data until the member chose to edit their record or renew their membership (if not previously edited) at which point the user would be required to replace the old non-compliant data value with a new one from the pick list. 

Another related feature that I'd like to see is the ability to dynamically switch a currently created field's type. 

Current Behaviour: I have an existing membership field textbox created called Province with specific Access and Use In options set for what membership form its included on, etc.  I decide I want to change its type to a drop-down-list.  To do this, I have to delete it and then add a new field called Province as drop-down-list and reset all the initial options again.

Future Behaviour: I can simply change the fields type after it is created to whatever type I want preserving the Access and Use-In options.

As you can see, there have been a lot of threads over time about this issue.

I've merged these into this one thread, and updated our internal tracking and analysis on this to reflect the demand for this feature.