Can I amend the specification to refer to a CPA as a continuation of a prior application?

No, you cannot amend the specification to refer to a Continued Prosecution Application (CPA) as a continuation of a prior application. The USPTO explicitly denies such amendments. As stated in MPEP ¶ 2.34:

The amendment filed [date] requesting that the specification be amended to refer to the present Continued Prosecution Application (CPA) as a [continuation/divisional] application of Application No. [X] has not been entered. As set forth in 37 CFR 1.53(d)(7), a request for a CPA is the specific reference required by 35 U.S.C. 120 to every application assigned the application number identified in such request. Thus, there is no need to amend the first sentence(s) of the specification to refer back to the prior application and any such amendment shall be denied entry.

This means that the act of filing a CPA automatically establishes the necessary reference to the prior application, making any specification amendment unnecessary and prohibited.

For more information on CPA, visit: CPA.