Position of adjectives

You cannot use “the present students” and “the students present” interchangeably.  For example, you can say:

The present students are excluded.

Or

The students present are excluded.

Both sentences are correct.

However, not all adjectives function as immediate post-modifiers of nouns.  For example, you can say

The clever students are excluded.

But you cannot say

The students clever are excluded.

Like you said, a difference in an adjective’s position can result in a difference in meaning.  Notice the semantic difference between the following sentences:

1.    The present minister does not approve of the draft resolution.

2.    The minister present does not approve of the draft resolution.

In sentence 1 “present” means “current”.  The minister might be in the presence of the speaker at the time of speaking, but he is still occupying the post of the minister  In sentence 2, “present” means “being at the same place of the speaker.”

The meaning is different.