[SDPhantom]

You can just call button:SetAttribute() again when you need to update it. This can't be done during combat however.

For example:

local button=CreateFrame("Button",nil,aura_env.region,"SecureActionButtonTemplate");
button:RegisterForClicks("LeftButtonUp","RightButtonUp");
button:SetAllPoints(aura_env.region);
 
button:SetAttribute("*type1","target");
button:SetAttribute("*type2","focus");
button:SetAttribute("unit","none");--   Special UnitID for "no unit"
 
button:RegisterEvent("PLAYER_ROLES_ASSIGNED");
button:RegisterEvent("GROUP_ROSTER_UPDATE");
button:RegisterEvent("RAID_ROSTER_UPDATE");
button:RegisterEvent("PLAYER_REGEN_ENABLED");
button:SetScript("OnEvent",function(self)
    if not InCombatLockdown() then--    Can't update in combat
        local unit="none";
        if IsInRaid() then
            for i=1,MAX_RAID_MEMBERS do
                local raidunit="raid"..i;
                local raidid=UnitInRaid(raidunit);--    Unit-to-ID mappings aren't guaranteed
                if raidid and not UnitIsUnit(raidunit,"player") and (select(10,GetRaidRosterInfo(raidid))=="maintank" or UnitGroupRolesAssigned(raidunit)=="TANK") then
                    unit=raidunit; break;
                end
            end
        end
        self:SetAttribute("unit",unit);
    end
end);