That's what the law says.  It says "gross income of such taxpayer shall not include so much of the unemployment compensation received by such taxpayer (or, in the case of a joint return, received by each spouse) as does not exceed $10,200."

I don't see anything that says it is optional.

One other word of warning ... I know that you have been manually adding the deduction, but have you been avoiding returns that involve some of the things that use MAGI that are NOT affected by the $10,200 exclusion?  Probably the most common one is how much Social Security is taxable is based on MAGI, which is based on the full amount of Unemployment (the $10,200 exclusion is not used).