[EKS] [request]: Managed Worker Nodes Ability to Change Instance Type without Replacement via Cloudformation

### Community Note

* Please vote on this issue by adding a 👍 [reaction](https://blog.github.com/2016-03-10-add-reactions-to-pull-requests-issues-and-comments/) to the original issue to help the community and maintainers prioritize this request
* Please do not leave "+1" or "me too" comments, they generate extra noise for issue followers and do not help prioritize the request
* If you are interested in working on this issue or have submitted a pull request, please leave a comment

**Tell us about your request**

We want to change the InstanceType List of an Existing Manageg Worker Node Group without Recreating it.

**Which service(s) is this request for?**
EKS

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**

We tried to set the Instance Type via the Launch Template. But there we cannot pass a list of InstanceTypes and are sticked to one InstanceType for each Node Group.

**Are you currently working around this issue?**

Wer are still using normal AutoScaling Group with EC2 Fleet

**Additional context**

We already asked AWS Premium Support which told us to use a Blue Green Approach to change the Instance Types. This is way too complex for such a little operational task. Furthermore, it is complicated to use this Approach with Cluster-Autoscaler and Priority Expander.

The issue names no repository files, tests, or entry points. Start by reviewing EKS managed worker node groups, Launch Templates, and CloudFormation constraints described here; done means an existing group can accept a changed InstanceType list without replacement.

Written by the indexing model from the issue text.