How can I control a custom parameter in QGIS WMS/WMTS/WFS webservices

GeoServer layers can be configured to be very flexible with parameters in at least these two ways:

• viewparams pass through to the SQL view (link)
• time/elevation/custom dimension (link and link)

A sample call would look something like: http://localhost:8080/geoserver/topp/wms?SERVICE=WMS&VERSION=1.1.1&REQUEST=GetMap&FORMAT=image%2Fpng&TRANSPARENT=true&STYLES&LAYERS=topp%3Atasmania_cities&SRS=EPSG%3A4326&WIDTH=768&HEIGHT=641&BBOX=145.9588623046875%2C-43.378143310546875%2C148.0682373046875%2C-41.617584228515625&time=2012-10-13T00:00:00.000Z&elevation=1233.47&viewparams=low:20000000 (note: time & elevation & viewparams=low)

In a JavaScript client like OpenLayers or Leaflet, it is easy to add these additional parameters to the WMS request.

In QGIS, it is possible to use the Time Manager (up to v3.12) or the Temporal Controller (after v3.12) to manipulate the time parameter (but the time parameter must be in the correct ISO8601 timestamp format, so can’t be used for general parameters)

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However, I cannot find another QGIS plugin that allows a user to manipulate any dimension (e.g. elevation or the low viewparam above) with a slider or similar control.

Can anyone point me in the right direction?

If not, is this something useful that I should consider implementing as a plugin?

I assume that I should be able to intercept the WMS/WMTS/WFS webservice requests when they are created, modify the parameters and forward them on.