I'm afraid your approach is wrong/confusing...
1. Shouldn't Web template files have .html extension?
I came to this topic because I'm currently trying to do that exactly the way you displayed here (by creating a plugin on layoutRenderer and modifying elementTmpl property.
In my case it would be
$result["components"]["checkout"]["children"]["steps"]["children"]["billing-step"]["children"]["payment"]
["children"]["afterMethods"]["children"]["billing-address-form"]["children"]["form-fields"]["children"]
["telephone"]['config']['elementTmpl'] = 'Magenteiro_FirestoreCustomizations/ui/template/form/element/telephone';
And my template file is currently located at `app/code/Magenteiro/FirestoreCustomizations/view/base/web/ui/template/form/element/telephone.html`.
I'm still getting error in the frontend ...
[ERROR] Failed to load the "Magenteiro_FirestoreCustomizations/ui/template/form/element/telephone" template requested by "checkout.steps.billing-step.payment.afterMethods.billing-address-form.form-fields.telephone".
Ricardo Martins - Magenteiro.com
