Premade Level Progress Problem

Hi, i have a little problem, while i construct and program a simple space shooter.

How could or sould i make some a premade lvl that is easy changable?
Like changeing the order of enemies apear or when the boss comes.

I thgought about somthing like a long long string vor every level where each leter represents
a specific action: for example:


where 0 would be a 5 second nothing time, E a simple enemiy group, B another one, X a bonus and the Z the end boss.

So what do you think about it, or is there a better way.

greets Equal

I think that would work fine

if own.init == 0:
    own.init = 1
    own.string = "000x00B00Z"
    own.index = 0

letter = own.string[own.index]

if letter == "0":
elif letter == "x":

own.index += 1