How does a candidate look like when he applies for another PhD program while being enrolled in a program? Suppose, someone is enrolled in a PhD program in a university 'X' in, say, Serbia (totally hypothetical and suits my analogy).

After one year, after publishing 5-6 research papers, he thought that a West-European or North American PhD has greater brand value. So, he applies for a different PhD program in the same discipline/topic.

How would the selection committee perceive about this particular candidate as opposed to someone just came out of a masters degree?
Wow. Five or six papers in the first year???? My alarm just went off. I don't know of any field, actually, in which that is possible and have those papers have much merit. If they are good papers, the candidate will be sought after nearly everywhere. But I'm going to doubt without evidence, including who published the papers. (see caveat below)

However, many students change universities in the middle of doctoral studies and for many reasons. Wanting to change countries or even regions of the same country is a common reason. 

This person will be judged in the same way that everyone else is: are they highly predicted to be successful in this program and what is the evidence for that. The background coursework will be considered as well as how they did. Any research experience? How good are letters of recommendation, etc. 

Those papers, if they exist, would be evidence, of course, but possibly not positive evidence. But even zero papers in the first year is unlikely to be of much importance in most fields. Association with a lab that produces hundreds of papers a year and each paper has hundreds of co-authors would be an exceptional case, of course. But most of those co-authors play a relatively minor part in the advancement claimed in the papers. 

Any application should be focused on those positive predictors of success, not the fact that the person is changing and not on the reason they are wanting a change.