Some grammar issues aside, the meaning of your sentence examples is arguably the same.
What you're describing is the difference between regular adverbs and flat adverbs:
an adverb such as ‘quick’, ‘slow’, ‘wrong’, or ‘different’ which has the same form as its associated adjective. For example in the sentences ‘Take it easy’, ‘Tell me straight’, ‘Don’t drive so fast!’, and ‘Some people may think different’, ‘easy’, ‘straight, ‘fast’, and ‘different’ are flat adverbs. Some flat adverbs such as ‘easy’, ’different’, ‘quick’, ‘slow’, and ‘wrong’ have a more usual form ending in ‘ly’ as in ‘easily’, ‘differently’ ‘quickly’, ‘slowly’, and ‘wrongly’.
Some people think that it is incorrect to use as adverbs forms such as ’quick’ and ’slow’ that also have a form ending in -ly.
However, whether or not flat adverbs are grammatical is somewhat debatable—depending on how you define either side of "use" versus "acceptability," and which specific adverb is being discussed.
The use of flat adverbs was more common in the past—and they were often thought of as adjectives instead. But their use has since grown much less common.
Mostly people take no issue with street signs that read Go slow but others think that they should instead read Go slowly.
While you could try to argue that the use of a very uncommonly used flat adverb is still "correct," you would find yourself with small company. On the other hand, you could try to argue that a very commonly used flat adverb is "wrong"—and would find yourself with equally small company.
It depends on each specific instance, and how "in line" you want to be with common opinion over that instance.
As has already been mentioned, you likely mean to use the word unattended rather than unintended. But there is no such word as unattendedly, so it's a poor example of what you were trying to express.
However, most people would say:
Don't leave your belongings unattended.
Don't take it personally.
While don't take it personal is used in some informal speech (and it's understood), it's not something that most people would recommend be used, and it certainly wouldn't be used formally.
