Altering char(2) to char(4) causing entire table rewrite?

I need to alter a char(2) field in a table to char(4). At present this column is null for all rows in the table (over 3 million rows, total table size around 300MB.)

However, when I attempt to make the change, it looks like it is rewriting every row in the table, because it is producing great quantities of archive logs. This brings my production users to a grinding halt.

Is there any way around this, or am I going to have to schedule this modification to run over a weekend?

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Mike Nolan
nolan_at_inetnebr.com