Can you program an attiny 85 after is soldered to a board?
Sure, if you plan ahead a bit. Pretty much every modern MCU family supports &quot;in-circuit&quot; (or &quot;in-system&quot;) programming, usually involving just a few pins. You just need to bring those pins out to a connector, and make sure that any other I/O functions that might be connected to them won't interfere with (or be adversely affected by) the programming protocol.
Sometimes a manual jumper or two is required on really low pin count devices if you can't otherwise arrange the I/O as needed.