how to castsequence+Modifier+Reset.

[Setith]

/castsequence [mod:alt] reset=2 charge, rend
/castsequence [nomodifier:shift] reset=4 Mortal Strike, Colossus smash, overpower, heroic strike

In this macro, 2 command react with mod:alt because with "nomodifier:shift", mod:alt it's ok

For other sequence without modifier try this :

/castsequence [mod:alt] reset=2 charge, rend
/castsequence [nomod] reset=4 Mortal Strike, Colossus smash, overpower, heroic strike

or

/castsequence [mod:alt] reset=2 charge, rend
/castsequence [nomod:alt] reset=4 Mortal Strike, Colossus smash, overpower, heroic strike