AWS::CloudFormation::CustomResource - ServiceToken-update

## Scope of request

Currently, updating a ServiceToken requires the custom resource to be renamed. Being able to update with [replacement](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/using-cfn-updating-stacks-update-behaviors.html#update-replacement) would simplify maintenance on the underlying lambda function.

## Expected behavior

Changing ServiceToken without renaming the resource in the CloudFormation template works, replacing the resource

## Suggest specific test cases

A CloudFormation template which takes a ServiceToken as a template parameter and contains an `AWS::CloudFormation::CustomResource` using that token. Update the token without changing the template.

## Helpful Links to speed up research and evaluation

The documentation page currently says both "Updates are not supported." and "Update requires: Replacement"

## Category

Management & Governance

Start by reproducing the suggested CloudFormation template with ServiceToken supplied as a template parameter, then update the token without renaming the custom resource. Read the linked CloudFormation update-behavior documentation and compare its statements about unsupported updates and replacement. Done means the token change succeeds and replaces the resource.

Written by the indexing model from the issue text.