You may need LabTalk script after import for such. On the last page of the import wizard, check the box Save Filter and Specify advanced filter options. Then click Next button. In the next page, enter the following script. Change ln to the longname of the columns to be set to x.
for (int i = 1; i < wks.ncols; i++) {
if (wks.col$(i).lname$ == "ln") {
wks.col$(i).type = 4;
}
}


James