Suppose I created a new project with 16:9 at 30 FPS and started working on it.
If I later realize that I need to convert the project into a 1:1 (square) instead of 16:9. OR opposite scenario, where I want to change from1:1 to 16:9. I would do that in Project Settings, but it gives a warning like:
This can’t be undone. Save your project because it might cause corruption in transitions
So is this the only way to do this or there is a better and safer way?
Hi, and welcome to the forum and community.
This is the only way to change it after you started on your project. It is a warning because some things may break, for example transitions, transformations or keyframes.
I say may, because most of the time it simply works but there could be the odd thing that doesn’t afterwards. You have been warned 
Therefore, making a copy of the project is highly recommended.
There’s a lot of Devil in the Details depending on why you want to change it and what result you want to obtain.
I’d generally be inclined to create/keep the project set at whatever your source clips actually are, and then if you want to render your editing in some other format or size look at the rescaling and aspect ratio options in the render dialog.
Well simple reason. For a particular video, one may not like 16:9 and prefers to crop into a square version because of demand by client. Of course you can’t always pre plan it. Priorities/preferences/taste change, no? I’d try the aspect ratio thing.
Change aspect ratio in the render dialog. But if the new aspect ratio requires cropping and therefore shifting focus or zooming, you have to go back to the timeline.
(Edited: Changing aspect ration is already available since 24.05)
I tried aspect ratio settings in render and at times it can be useful. But for my current requirement, I need to do a lot of panning/transformation and zooming so, it was better to change the project settings.
Yeah, that’s why I said the best approach can depend on what you want to achieve.
One thing to be careful with is that some effects, and some stacks of effects, can behave unexpectedly and unintuitively when kdenlive has ‘automatically’ rescaled your source material from its original dimensions and aspect to your project configuration.
Which is why I suggested it still may be better to have your project match your source material, even if the transforms you apply to it are done with an eye to rendering in a different aspect to what you are editing in.
You can see one case of that happening described (along with a link to the roadmap recognising the problem and desirability of fixing it) here: