The author has done some good work ensuring good design practices; trace separation, fuses, etc. but I don't see any extra I/O brought out on this particularl switch. You would have to carefully solder to the chip itself, and modify the code a bit.
You could use magnetic switches. Put a magnet on the blinds and the switch in window sill.
The author notes that this is not an Arduino, but uses the same chip that the Arduino uses. The author doesn't explain how the chip is programmed. This method could have been used.
It may be just as easy to use an RF Nano with a little power supply. This suggestion is not nearly as robust as the author's. For example, these power supplies have gotten bad reviews mainly because the mains power traces are too close together. I justify using them because in all likelihood a failure will pop the power supply and probably the Nano, too, noting that these are cheaper than the fuses you would put in to protect them. I am fully aware of the risks involved in doing this, and you should be, too (eg. burning down your house).
-OSD
@Michael-Link I have been out of touch with MySensors for some time now and looking to slowly get back into it. I created this and a few other boards back in 2018 All of the GERBER files for this are in the "Design Files" tab. Those you should be able to send to JLC PCB or one of the other fab houses and have some made. This was designed to be used with 2 other boards that I designed. There was the processor board and the power supply board. The processor board was designed in a way that I could use a couple different switch boards. This one and a universal multi-switch board that had multiple configurations. If you look here you will see my other boards.
