See https://www.law.cornell.edu/cfr/text/26/1.266-1

§1.266-1(c)(3)

If the taxpayer elects to capitalize an item or items under this section, such election shall be exercised by filing with the original return for the year for which the election is made a statement indicating the item or items (whether with respect to the same project or to different projects) which the taxpayer elects to treat as chargeable to capital account.

[emphasis added]

@Tronathan