I don't think you have to write a statement to opt out of form 3115, you just don't file one. Businesses still have to make the changes going forward, but the form is no longer necessary, businesses simply indicate they adopted the standards by doing what the standards require.
this article might be clearer –
https://www.kpmg.com/US/en/IssuesAndInsights/ArticlesPublications/taxnewsflash/Pages/2015-1/rev-proc-2015-20-accounting-method-change-relief-for-small-business-taxpayers.aspx
“The IRS noted that some small business taxpayers may choose to file a Form 3115 in order to retain a clear record of a change in method of accounting or to make permissible concurrent automatic changes on the same form, whereas other small business taxpayers may prefer the administrative convenience of being able to comply with the final tangible property regulations in their first tax year that begins on or after January 1, 2014, solely through the filing of a federal tax return.
Accordingly, for the first tax year that begins on or after January 1, 2014, small business taxpayers that choose to apply the tangible property regulations prospectively to amounts paid or incurred, and dispositions, in tax years beginning on or after January 1, 2014, have the option of making certain tangible property and dispositions changes in method of accounting on the federal tax return without including a separate Form 3115 or separate statement.”
FAR: 55, 52, 66
REG: 84*
AUD: 54, 70, 73, 72, 79!!!
BEC: 75*
*expired
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