TFS: how change fields "Found In Build" and "Resolved in Build" to integer

Question

My intention is to change type for "Found in Build" and "IntegrationBuild" field types from string to integer. I had a similar task to do: create string field for "Priority" field (http://stackoverflow.com/questions/3834191/how-do-i-create-new-field-of-string-type). For that I got suggestion to create additional custom name of string type and update original integer type with a special 'rules'.

• Q1. Do I need to keep in sync "old" field with a new custom fields?
• Q2. Could I use ANY string value for "Microsoft.VSTS.Build.FoundIn" and "Microsoft.VSTS.Build.IntegrationBuild"?
• Q3. Is it good to delete 'SuggestedValues' rule for these field?
• Q4. What is a conversion rule for conversion from integer to string?

Any thoughts are welcome.

Thanks!