Furniture, Wood and Cabinetry Finishing - Replacing Individual boards

I'm pretty handy, was wondering how difficult it is to replace individual hardwood boards?

are all unfinished oak boards the same and will finish the same when I add the new pieces?

No, they're not all the same is size. Unless you're used to working in 64th inch and beyond, and can use a tablesaw, the new boards won't fit well.

Same wood species and grain profile will blend in just fine.

1/4" thick oak strip, pretty easy.

3/4" tongue&groove stuff, very difficult. *Nearly* impossible to fix invisibly.

A trick that usually works is to remove boards from closets. They will match in size, age, and grain. Removing a board is not too difficult, but the first one is destroyed. Cut a board lengthwise down the center, setting the saw to only cut the board depth. Pry it out being careful not to damage the tongue/groove of adjacent boards. Cut the bottom of the groove of the replacement board, this allows the tongue to slide in and gently hammer down the board. Finish nail, and set, then putty the nails.