Update Column Without Changing Datatype?

I am trying to make the following update: All the columns are fine except for the 'name' column. datatype for 'name' column in the target table is varchar(30) and the datatype for 'name' in the sourcetable is varchar(40), I cannot change the datatype of the column 'name' to varchar(40) because I am told it may affect performance. what I want to do is just update the first 'name' column of the target table by the first 30 characters of the source table column 'name'

I am using the following query, is it possible to do it or are there any other ways I can update the column without changing the datatype?

MERGE INTO [S].[dbo].[AF_Copy] AS TargetTable
USING (SELECT source_code, name, addr1, city, zip FROM
[D].[D_TEST].[dbo].[SO_Copy]) AS SourceTable
ON ([TargetTable].[Code] = [SourceTable].[source_code])

[code]...