I changed a word from a source, how do I cite it correctly? I'm writing an analytical summary on Meditation II of Descartes from the compendium we have been given at school. We have been told to use this as our main source. Nevertheless, there is this specific part in section 12 of that meditation which I don't quite agree with:


  [...] something extended, flexible and movable.


As per Marleen Rozemond in Descartes' Dualism [Source] in page 93, this is a poor translation.

The reason I looked this up was because the word didn't quite fit the context, and then I saw other people had translated it as mutable, which is also a correct translation for the french/latin word.

Complaining about the poor translation in the summary makes little sense to me, as it's not part of the context, and I have a limitation of 600 words to care about. Nevertheless, I am citing from the source of a document which uses the "movable" word instead of the "mutable" word.

How should I approach this? Should I make a postdata explaining why I have done what I did?

For reference, I am using the APA referencing style.
Write:


  [...] something extended, flexible and [mutable].


You might like to elaborate in a footnote, e.g., 


  The compendium poorly translates original word as movable, but mutable is more appropriate, as noted by Marleen Rozemond in "Descartes' Dualism," page 93.


(Depending on the style, you might like to replace in "Descartes' Dualism," page 93 with a citation.)