Changing the type of a SFDC field is one of the reasons why landing pages are put into draft mode automatically by Marketo.

 

Change to Field

Marketo Form Automatically Re-Approved

Marketo Landing Page Automatically Moved to Draft

Length of text field increased

Yes

Yes

Length of text field decreased

No

No

Field type changed from Text (50) to Text Area (255)

Yes

Yes

Field type change from Text Area to Text

No

No

Picklist changed

Yes

Yes

Field type changed from Picklist to Text

No

No

Field type changed from Text to Picklist

Yes

Yes

 

In all the cases above the field type in Marketo will remain a string. Since the field type won't need to be changed in Marketo the values of the field will remain.

 

If you change the type of a SFDC field from text to checkbox or date/time, the field type change doesn’t happen automatically in Marketo. A manual change is required in Marketo in order to properly sync to the right field type. When you change a field type in Marketo the data may be deleted. To preserve the data, you will want  to export it and re-import it after you change the field type. You may need to change the format of the value, depending on what the date field will accept and how the value is formatted now. In order to change the field type you'd need to remove it from all assets currently referencing it as well, so if you have a lot it might be easier to create a new field and start using that one instead.

 

Marketo change field type article.

 

When the length of a field is changed you should see the following notification in Marketo:

Subject: Salesforce Sync Warning: Change in Salesforce Field

Why: One or more fields has been changed in Salesforce.com

Error details: The following fields have been changed:

•  System of Interest

•  maximum length changed - old value: '50', new value: '100'

These fields appear in the following forms/landing pages:

APAC-JP-2015-05-10 Getting Started Webinar - Assets.01 Registration Page

 

When a picklist is changed you should see the following notification in Marketo:

Subject: Salesforce Sync Warning: Change in Salesforce Field

Why: One or more fields has been changed in Salesforce.com

Error details: The following fields have been changed:

•  Industry picklist entries changed

These fields appear in the following forms/landing pages:

• NAM-2016-04-11 Webinar - Assets.01 Registration Page

 

Finally, here is information about changing the type of a field using Marketo.