Is a defendant required to obtain a certificate of probable cause to challenge a sentence imposed after a no contest plea?

In a supplemental brief we requested, defendant argues he did not need to obtain a certificate of probable cause because it is only necessary where the challenge goes to the validity of the plea, not where, as here, he seeks only a modification of some terms that "will in no way undermine the substance of the plea agreement[] . . . [but] will further secure the validity of the plea agreement by making the probation conditions lawful, enforceable, and consistent with the intent of the parties." "In determining whether [Penal Code] section 1237.5 applies to a challenge of a sentence imposed after a plea of guilty or no contest, courts must look to the substance of the appeal: `the crucial issue is what the defendant is challenging, not the time or manner in which the challenge is made.' [Citation.] Hence, the critical inquiry is whether a challenge to the sentence is in substance a challenge to the validity of the plea, thus rendering the appeal subject to the requirements of section 1237.5. [Citation.]" (People v. Panizzon (1996) 13 Cal.4th 68, 76.) Here defendant does not challenge the sentence or the substance of the plea but only the breadth of some conditions. But this does not dispose of the issue of the failure to include this issue in the notice of appeal.