I'm making a change in the software which should be unnoticeable to users. What would be a single word that describes it best? I'm looking for an adjective that fits into sentence such as 'This change will be _____ to the end user.'
In software and hardware engineering the term would be "transparent".
Some devops heavyweights release software updates thousands of times per day — often so transparently that their users are not even aware.
Transparent things can be noticeable. A sheet of glass is transparent/translucent, but may be very noticeable. More transparency leads to less noticeability (thus the answer above talking about 'so transparent' (transparent would not need a quantifier if it was absolute).
Things that cannot be seen are invisible.
You're making a metaphor: if you use invisible or transparent, you're implying it would have been something someone else sees, or that the change would be something seen and not "felt" or "experienced."
So I disagree with using invisible/transparent. But one of the reasons you're in this rut is that you've started with this format:
'This change will be _____ to the end user.'
You're also loading the question by using "_____ to" instead of "_____ by" or "will be _____" instead of "will not be _____."
You're also making a statement about the 'end user' but what about the end user, specifically?
What about "This change will not impact the end user's experience."
That covers 0 performance change, 0 visual changes and does not make a physical metaphor about deployment or ideas towards the software.
If the format is a hard requirement, perhaps:
"This change will be inconsequential to the end user." But, is it? Does it actually make something else more efficient which in an indirect manner does have consequences for the user?