Action to alter webform element

Have you tried using the Build form event to alter the form like any other form in Drupal?

That event would work as well, but that doesn't change the fact that there are no actions to make the alterations I require; it seems webform is using some webform-specific element attributes that are not present in Drupal Core form elements.

Additionally, the ECA Form actions seem to be limited to changing the disabled state, accessibility, weight, options and label of the field; there is no way to alter other element attributes. There are also no actions that would allow ephemerally altering the widget or field settings ahead of the form build.

That's correct @starlight-sparkle. When providing new action plugins to allow for more options, then we should always carefully determine whether this would be Webform-specific or maybe generic. For the latter, enhancements should go into the eca_form submodule, others would be best in here.

Contributions are very welcome. I'll be helping with questions and reviewing MRs, I just don't have the resources available to build such features myself in the short and mid term.