Default or prevent ADF Pipeline Activity Parameters - azure-data-factory

Question

How do you specify that an activity should not be parameterised in an exported ARM template, or ensure the parameter default value is whatever is already specified?
I have an ADF pipeline which contains a WebActivity. This WebActivity URL is set by an expression which concatenates some text with some pipeline parameters:
#concat(pipeline().parameters.URL,'path/',pipeline().parameters.ANOTHER_PARAMETER,'/morePath/', pipeline().parameters.YET_ANOTHER_PARAMETER,'/lastBitOfPath')
When I export the ADF template through the UI, there are some parameters added which look like: PIPELINE_NAME_properties_0_typeProperties, are type String, but are blank. These appear to correspond to the WebActivity URL fields in various activities.
If I then import that ARM template and parameter file into a new Data Factory, the WebActivity URL is blank. This means I need to override the parameter as normal, fine, but why....? I don't need a new parameter to specify a value that is already set by parameters... how do I ensure that this activity is imported with the same expression? It seems mad that to use a WebActivity means you have to parameterise the expression. I want the ARM Template > Export ARM Template to export what I've got, not add redundant parameters that I do not need.
I have also tried editing the pipeline JSON to add a default and defaultValue attribute for the URL activity, but they are removed and have no effect.

Answer 1

It seems the reason for this is that the parameterization template has been modified to include:
"Microsoft.DataFactory/factories/pipelines": {
"properties": {
...
"activities": [{
"typeProperties": {
"url": "-::string"
}
}
]
}
},
Which removes the default for all URL properties of all activities.
https://learn.microsoft.com/en-gb/azure/data-factory/continuous-integration-deployment#use-custom-parameters-with-the-resource-manager-template
This applies to all activites so it seems the only alternative is to specify
"url": "=::string"
Which will parameterise the URL (so any existing parameterization will continue to function) but keep the original value by default. Care must then be taken to override any other activity url properties that I do not wish to move.