When you have been in manufacturing long enough, you begin to recognize a few common themes. Four buckets, if you will, for the problems to collect in.
When it comes to Engineering Changes or Process Changes, here are the 4 buckets that come to my mind.

Mistakes when considering changing a process fall into 4 buckets

Bucket Number 1– Claiming savings that don’t really exist. I also call this Green Belt Fantasy #1, and Boss Delusion # 1. Typically the savings or “improved performance” aren’t sustained if they show up at all. The academic name for this bucket is the Hawthorne Effect, or the “Observers Paradox.”
Bucket Number 2– Ignoring labor fringe benefits (and overhead.) This can easily be 20% or more per labor dollar and just because the accountants claim they have it figured in doesn’t mean they do.  Overhead is a dumpster itself of hidden problems, buried corpses -err, costs-  that always has its own persistent odor.
The fraternal twin of this is failing to account for unanticipated maintenance costs. I call this bucket the Iceberg Bucket because you only see a tiny part of the real problem.
The Iceberg bucket.
Bucket Number 3– Using production time estimates that reflect substantially different rates of work. The best example of this that I can recall was in a movie where the  producer had a time study of how a chair was being painted (by brush) so he could low ball the quote. (He needed a bunch of chairs for his production.)  After the producer got his lowball price accepted,  the painting contractor picked up his signed copy of the contract and hollered to his crew “SPRAY EM!”  In our industry we wouldn’t dream of using setup time estimates for a cam machine on a CNC  machine, but…
I call this  Bucket Number 3 the Apples to Oranges Bucket.
Apples to Oranges

Bucket Number 4 is the most trying of all.  We all like to think that we make decisions on the basis of cold hard facts and rational decision making. But research with people whose brains have been injured  have shown that their purely cold hard rational decisions with no emotional inputs almost always tend to be poor ones. Our mental processes have a lot more adrenalin and other “chemical inputs” than we will admit. If we really want to make a project happen, we somehow manage to ignore, under weigh, or fail to consider unquantifiable critieria, especially relating to human performance issues of those affected.  Employee fatigue, effort required, distractions effect on performance, and job disatisfaction. I call this bucket The Invisible Bucket because it holds the  costs of change that you cannot see and cannot measure- disruption, resistance to change, adjustment time, learning curve issues  etc…  All of these are  invisible at the time when you most need to see them.
The Invisible Bucket!

Worker acceptance of change is difficult to predict. It is even more difficult to manage.
But the key in my experience to eliminating all of these buckets is to get the employees that have to do the work a contributing role on the team to implement the change.
Become the change you wish to see”  and “The easiest way to deal with change is to help create it”  are 2 truisms that can help your people  get involved and so avoid dealing with the 4 ugly buckets described above.
How do you avoid tripping over these buckets in your operations?
4 Buckets
Apples to Oranges
Invisible bucket (I did the photoshop)