Answer
No reinstall needed — edit ifs-crystal-config.xml directly, found under C:\inetpub\wwwroot\<YOUR_CRYSTAL_INSTANCE>\, and update its <DB_PASSWORD> element (and <PRINT_PASSWORD> if that account's password also changed) with the correct current encrypted password values for the target environment. Those correct encrypted values can be copied directly from the corresponding environment's own configuration.xml file (under <IFS_HOME>\instance\<INSTANCE_NAME>\) — specifically its <ifs.system.password.encrypted> and <ifs.ifsprint.password.encrypted> entries — pasted straight into the matching fields in ifs-crystal-config.xml, with no need to reinstall or reconfigure Crystal Web Service itself.