I would suggest you contact your Cisco & Meraki partner account team - and also similar for the big customers in question (to get more weight behind your ask).
I can't help thinking also that, if you're wanting to automate your processes using API, why not do that for all the Networks, individually, rather than manipulating Templates via API as an interim step? I can see you have big customers, which may make a difference, but it's generally the case that people use Templates until they doesn't really do what you need (and most can keep the number of Templates to a manageable number, where they work ok) but then move solely to API, to manage at scale, if not.