As far as I know, there is no "hacked" or modified firmware available for your camera. The most popular firmware, Magic Lantern, is not supported for your camera.

Therefore, your only options are to either learn to more about your camera's features and controls, or upgrade to a different camera that allows for manual focusing.

In my opinion, you don't need to upgrade your camera. I think you can probably achieve what you want with your current camera. The most important advice I can give is to read the manual (link goes to Canon's USA site for your camera), and get comfortable with your camera's features and controls. I can't stress this enough. Sit down with your camera and the user manual, start from the beginning, and perform every setting, control, etc., that the manual says the camera can do. You will only learn by doing.

When taking shots with your camera like the ones you posted, I would do the following:

1. Use "Center" AF Frame Mode: (p.55 of the manual) This will restrict autofocus to only use the center of the frame. The camera will not focus on motion or objects outside of the center area.

2. Reduce the AF frame size: (p. 55 of the manual) You can reduce the size of the autofocus frame in your camera. This will make the camera focus only on a smaller portion of the frame. This will help you when trying to focus on the squirrel, for example, which is partially obscured by branches in front of it, by more accurately "pinpointing" the squirrel instead of parts of the tree.

3. Use AF Lock: (p.58 of the manual) Focus on your subject by half-pressing the shutter button while aiming at the subject. When you have your subject in focus, while still holding the shutter button half-way, lock the focus by pressing the left side of the multi-selector button (◀︎). This will prevent the autofocus from changing the focus, until you press the left button again. With AF Lock, you can take multiple shots without the focus changing.

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Edit: As StephenG's answer details, CHDK has at least alpha-release support for the SX410. If you are interested in going the CHDK route, that will certainly provide the manual focus override you are looking for. The rest of my answer details how to control focus without needing to use firmware modfications.