How to rename, in an XML file, specific tags that are embedded in some other specific tags

What is the xmlstarlet command to replace a tag value by another one, only for specified tags embedded in other specified tags? Example: searching every occurance of the tag b, that needs to be replaced by d only if it is within the ... tag (inside other tags): * Input example:

This is an example. This is a test;

* Desired output:

This is an example. This is a test;

This post is related to https://unix.stackexchange.com/q/700179/523366 in the solution I am trying to find to format xml files.