This is what the rule says (Appendix 5.1 of
the current regs):
A manufacturer may apply to the FIA during the course of the homologation period to carry
out modifications to the homologated Power Unit elements for the sole purposes of
reliability, safety, cost saving, or minimal incidental changes permitted in 5.4 below.
Applications must be made in writing to the FIA Technical Department and must provide all
necessary supporting information including, where appropriate, clear evidence of failures.
The FIA will circulate the correspondence to all Power Unit Manufacturers for comment.
If the FIA is satisfied, in its absolute discretion, that these changes are acceptable, they will
confirm to the Power Unit Manufacturer concerned that they may be carried out.
Wherever practical, such requests must be submitted at least 14 days before the requested
date of homologation.
The procedure and associated document templates that must be used by the Power Unit
Manufacturers for their requests are available in the Appendix of the Regulations.
It does not require agreement from other engine manufacturers, only comment. As we've seen before during homologation periods the teams will take advantage of this, and those reliability gains will lead to performance improvements.