can i repeat the case twice with different command like this code?

customKey = customKeypad.getKey();
if(customKey)
{
switch(customKey)
{
case '':
//do something...
if(customKey)
{
switch(customKey)
{
case '
':
//do something...
break;
}
break;
}
}
}

That code makes no sense. If a key was pressed, and it is a '', you can do any number of things in the case section. Testing that there is still a key and that it is still '' is a silly thing to do. Once the value in customKey is determined to be '*', it doesn't change, so the if statement will still be true and the same case will be selected again.

What problem are you trying to solve ?

I have assigned all of the keys with conditions... I thought it might be possible to use the key twice with different conditions because I want to add another condition but within a used key...

How about detecting long and short keypresses to give multiple functions ?