With the release of the second edition of Yomi, designer/publisher David Sirlin released a small upgrade pack that consisted solely of those cards with changed gameplay values and details. Those cards are:
Grave 10
Jaina red(2,3,5,6) 7, 10, J
Midori K
Setsuki 10
Rook 3, K
Valerie 10, K
Lum 10, Q, A
Argagarg 10
character cards x10
Please be aware of several drawbacks of using these as an upgrade:
The latest cards have differently formatted ability boxes than the v1 cards. Now there's a timing tag in the upper right like "Draw Phase" that your old cards won't have, so the new ability formatting won't match your old (unchanged) ability cards.
There's now a "normal draw rule." The help text of the new cards says to draw when your normal attack is blocked or wins combat. Your old cards won't say the right help text, but the new ones will.
Does not include art tweaks.
They do not include reworded abilities (which is basically ALL abilities). The new ones are shorter and more concise, partly due to the new timing tags.
They do not include the new stat reference cards.
Your old tuckboxes probably can't fit the extra EX cards inside, if you choose to get the EX Powerup, but the new tuckboxes can.
If these issues don't bother you though, you can use these v1 gameplay-changed cards to get to the latest balance and be tournament-legal. The graphic enhancements not included here are shown in the "Improvements since 1st edition" section on the Yomi Kickstarter page.