Thymeleaf pick json template based on input variable such as clientId

Question

I'd like to be able to configure different json templates based on e.g. a clientId with a default template in case a template for the clientId is not defined.

    Context context = new Context();
    
    Map<String, Object> templateResolutionAttribute = new HashMap<>();
    templateResolutionAttribute.put("clientId", 12345);//Trying to somehow pass a variable to the template selection process...        

    TemplateSpec templateSpec = new TemplateSpec(
            "json/data.json",
            templateResolutionAttribute
    );

    String output = springTemplateEngine.process(templateSpec, context);

The Spring Config class I'm using looks like this:

@Configuration
public class ThymeLeafConfig {
    @Bean
    public SpringResourceTemplateResolver jsonMessageTemplateResolver() {
        SpringResourceTemplateResolver theResourceTemplateResolver =
                new SpringResourceTemplateResolver();
        theResourceTemplateResolver.setPrefix("classpath:/templates/");
        theResourceTemplateResolver.setResolvablePatterns(
                Collections.singleton("json/*"));
        theResourceTemplateResolver.setSuffix(".json");
        theResourceTemplateResolver.setCharacterEncoding("UTF-8");
        theResourceTemplateResolver.setCacheable(false);
        theResourceTemplateResolver.setOrder(1);
        return theResourceTemplateResolver;
    }

The json templates could be in different directories or alternatively have different file names (whatever works best/easiest):

json/
  data.json
  12345/
    data.json

or

json/
  data.json
  data.12345.json

What is the best or easiest way to achieve returning a template that "matches" the clientId and if no match for the clientId is found return a default template?

Note: For new clients, ideally, I'd like to be able to just add new json templates without making any code changes...