Word or phrase meaning unnecessary work, not "busywork"

Question

In Chinese, there's an expression: 畫蛇添足 (literally: drawing a snake and adding feet to it). The phrase is used to describe a situation where you have completed the required task, but you do useless work on it anyway, resulting in you either missing a deadline (like the original fable), an unhappy customer, or both. I thought the closest equivalent to that was busywork, but when I was talking to a friend, he said I was using the word wrong, but he didn't know the right word either. Is there an English word or phrase that means the same thing?

Not a duplicate of this or the linked duplicate to that question either. Those questions deal with completing a task in a roundabout way. My question is about after they finish the task and do extra work anyway. Example: my company is tasked with building a computer, with a 1 month deadline. I finish building the computer within 3 weeks. My boss thinks I finished too early and wants me to (blank). I decide to come up with a way to make the computer talk. I either A: take too long and miss my deadline, B: irritate my client who just wants to type in peace, or both. (Ignore the unrealism of my example.)

Answer 1

An English idiom expressing this is

gilding the lily

Idioms gild the lily: to add unnecessary ornamentation, a special feature, etc., in an attempt to improve something that is already complete, satisfactory, or ideal:

After that wonderful meal, serving a fancy dessert would be gilding the lily.

[Dictionary.com]

There is also a single word, supererogation:

supererogation:

the act of performing more than is required by duty, obligation, or need

[M-W]

but it's used very rarely, and is impossibly formal in most situations.

Answer 2

If you put excess work into a task, you overdo it. From Oxford Learner's Dictionary:

1. overdo something to do something too much; to exaggerate something

2. overdo something to use too much of something

3. [usually passive] overdo something to cook something for too long ("the fish was overdone and very dry")

Often, something overdone is worse off than if the task or activity were merely done (examples from Merriam-Webster):

The acting in that play was badly overdone. (Overdone describes an excessively hammy or emotive style of performance)

Expecting that one relative who really overdoes it on the perfume or after shave? (The relative overdoes perfume, or applies too much of it, resulting in an overwhelming smell.)

Here is an example of the word used in reference to art and design (from an article entered into Congressional Record congratulating Charlie Daniel, an editorial cartoonist from Knoxville, Tennessee):

"Some of my earlier work was overdone," [Charlie Daniel] said. "I've learned to know when to quit a drawing. Just make your point and stop."