How to apply PowerPoint template (.POTX/.PPTX) to existing slides using python-pptx?

[umair-shahzad12]

I am developing a PowerPoint Add-in using the Office JavaScript API.

I want to apply a PowerPoint template (POTX or PPTX) to the user’s current presentation without adding or replacing slides — basically, I want to apply the new design/theme to the existing slides.
Currently, I am using office js API, this inserts new slides from the uploaded template, but it doesn’t update the existing slides with the new design.

Questions

Is there any support in python-pptx so that we can apply a POTX/PPTX theme to existing slides?

Can we copy or move content from an existing slide to a new slide programmatically?

Are there any plans to add such functionality in the python-pptx?

What is the recommended approach if we want to let users change slide design dynamically?

[MartinPacker]

(I'm not the developer but) I'd say pretty much the only reliable thing you can do is to give them a template presentation and do a call like

prs = pptx.Presentation("<my template pptx>")