Cannot override existing grok patterns

[piotrminkina]

I am trying to test Grok patterns on https://grokconstructor.appspot.com/do/match, but it turns out that it is not possible to overwrite existing rules. Reading the rule definitions on https://grokconstructor.appspot.com/groklib/haproxy, there are certain rules that are just begging to be overwritten. These are HAPROXYCAPTUREDREQUESTHEADERS and HAPROXYCAPTUREDRESPONSEHEADERS, because they depend on the specific HAProxy configuration. I wanted to test these patterns, as shown in the screenshot below, but the result is not what I expected.

(still captured_request_headers, but there is no request_header_host_short and request_header_host_domain).

In tools such as fstab/grok_exporter, overwriting works as expected, so I would be grateful if GrokConstructor also allowed overwriting existing patterns. Thanks in advance.