Hi,
 
JMP 17 doesn't change the column type after the import operation.  If you run the Source script that is generated from a table where the column has been manually adjusted once, you should see it come in as Character again. Here is an example of a script where the General column has been changed to Character.
 
Open(
	"$DESKTOP/Test Decimals Horizontal.xlsx",
	Worksheets( "Sheet1" ),
	Use for all sheets( 1 ),
	Concatenate Worksheets( 0 ),
	Create Concatenation Column( 0 ),
	Worksheet Settings(
		1,
		Has Column Headers( 1 ),
		Number of Rows in Headers( 1 ),
		Headers Start on Row( 1 ),
		Data Starts on Row( 2 ),
		Data Starts on Column( 1 ),
		Data Ends on Row( 1317 ),
		Data Ends on Column( 0 ),
		Replicated Spanned Rows( 1 ),
		Replicated Spanned Headers( 0 ),
		Suppress Hidden Rows( 1 ),
		Suppress Hidden Columns( 1 ),
		Suppress Empty Columns( 1 ),
		Treat as Hierarchy( 0 ),
		Multiple Series Stack( 0 ),
		Import Cell Colors( 0 ),
		Limit Column Detect( 0 ),
		Column Separator String( "-" ),
		Column Numeric Format(
			Index( 1 ),
			Column Name( General ),
			Datatype( "Character" )
		),
		Column Numeric Format(
			Index( 2 ),
			Column Name( Number 0 ),
			Format( "Best", 9 )
		)
	)
)