How to enable flash in Camera2 API without creating a new session?

Question

Android

Good day to all. I'm working on an application based on the Camera 2 API and I want to add the ability to enable/disable the flash in this application.
I know it can be done like this:

mPreviewBuilder.set(CaptureRequest.FLASH_MODE, CaptureRequest.FLASH_MODE_SINGLE);
mPreviewSession.setRepeatingRequest(mPreviewBuilder.build(), null, null);

But as far as I understand, creating a new session is a costly procedure and plus I don't want to lose frames from the camera.
Can you please tell me if there is a way to enable flash without creating a new session? I wonder how this is done in standard applications, maybe there is some kind of open source code (normally working)?
Or am I mistaken, and creating a session does not particularly require resources, etc.?
Thank you all in advance for your replies!