Modding: Spells

[Attle]

Am I too ambitious if I were to try to add the effect of the Illwinter spell to a summoning spell that I made. Is it possible?
The manual states:
"With this command the effect of another spell will
also take place when the effect of the main spell
occurs. The nextspell takes place on every area
where the main spell takes effect. So make sure
the area of the second spell isn’t greater than 1
or there will be overlaps."
In my case the main spell is a summoning spell which only works for Nifelheim. It summons one unique unit. The Illwinter spell being global has a bigger area I assume. Therefore making it impossible?
Were I to reverse the order. As in copying the Illwinter spell, make some changes and add a next spell to it. Would that make it possible?
I don't quite get this.I hope I have been able to explain myself.