@matkor it is currently not possible. https://github.com/mysensors/MySensors/issues/1312 suggests a solution but there has been no forward progress lately.

I ordered a batch from PCBs.io With the permission of the orginal author, I could enable sharing it there, which should reduce the price...

@tlustoch The node is a very simple one. So I never considered boot loaders, as the node would not need changing sketches during it's lifetime. I have boot loading functionality on my other designs, this one is a minimal board. Any extra chip would beat the purpose of the word "minimal". It's a dumb node for a reason :-)