Raj,
yes ofcourse you can export and import Extended fields from TN to another TN but the only issue is their values will not be loaded when you import,so again you have to select particular profile/ExtendedFields you will see the particular Group and fill the values eg:Group- EDIINT–AS1MDNURL like you might have Custom Group.
While exporting use the ExportData Show (All)then scrolldown until you seen the ExtendedFields (ICON)these will be in the last.So select the (Group)eg:EDIINT,Custom and push them to selected Items like you do the profiles/doctypes etc…
let me you if u are not clear…
HTH,
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