How to develop custom blocks without triggering validation errors

I am trying to create a custom block for text input field.

I managed to create a simple block that produces the <p> tag. When I change it to produce the <input> tag and refresh I am getting Block validation failed and the only solution is to remove the block and re-insert it.

It is ok if you have few blocks on a page but I am wondering what if I want to update a whole theme with existing content. Seems like even changing a trivial property as colour results in validation error.

What is the correct way of amending and updating existing Gutenberg blocks?