Nei, det er ikke!
Should "modify" be accepted too?
It could be. But in the meaning modify or alter, we also have the word "modifisere", which might be slightly more precise.
What is the difference between hearing og and å?
Why is "lett" used here?
You could also say "enkelt". In this setting they are interchangeable.
In which cases, should I say, for å AND when just that indefinite form?
If you can say "in order to" in English, you should use "for å".
In a previous sentence you said endre cannt be used instransively. But how about in this sentence?
In this case, we'll assume there's some context where "det" refers to something previously mentioned. Jeg vil ha smørbrødet uten tomat. Det [smørbrødet] er lett å endre.
Å endre hva? Et likt, ja. Deg, nei.
Does "enkel" work too?