The tax credits allowed under the Nebraska Shortline Rail Modernization Act may be assigned by the eligible taxpayer to another taxpayer by written agreement at any time during the taxable year in which the credit was first allowed for the eligible taxpayer or in the five taxable years immediately following the taxable year in which the credit was first allowed for the eligible taxpayer. The assignor and assignee shall jointly file a copy of the written assignment agreement with the department within thirty days of the assignment. The written agreement shall contain the name, address, and taxpayer identification number of the parties to the assignment, the taxable year the eligible taxpayer incurred the expenditures, the amount of credit being assigned, and all taxable years for which the credit may be claimed.