Sounds like you have 2 questions.

General Rule: Per Section 179 and §1.179-1 ..  A section 179 expense deduction for section 179 property shall be made on the taxpayer's first income tax return for the taxable year to which the election applies (whether or not the return is timely) or on an amended return filed within the time prescribed by law (including extensions) for filing the return for such taxable year

Regarding the Sec 179 deduction not changing business net income or client's taxable income ... it may be due to a limitation imposed by Sec 179 that prohibits that deduction from throwing the business income into a loss. Any unused Sec 179 claimed is carried over to next year. Therefore, if the business net income did not change because of that limitation, there would be no change in Client's taxable income or tax, but the Sec 179 carryover is locked in due to the original return having been filed.

Regarding necessity of filing an amended return ...  If you decide to change the Sec 179 deduction reported on their original 1040, an amended return is required and a 1040X can now be efiled.to claim the additional Sec 179 and claim the carryover of unused Sec 179 deduction.

BOTTOM LINE: If you merely change the cost basis and leave the Sec 179 the same, the taxable income and tax do not change, so there is no need to file an amended return. But the mix of regular depr and Sec 179 depreciation used will have changed so make appropriate changes so that next year is correct regarding regular depreciation used and unused and regarding the Sec 179 depreciation used and unused. If, however, you want to claim the additional 179 deduction and have it carryover, you need to do it on a timely filed amended return. In order to make the 1040X populate properly, follow the instruction in the HELP section of the program guide.

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