Hi. As you know, major companies allow people to apply to job offers on line. Recently, I applied to a job offer at IBM, I created a profile for me and uploaded my CV. Suppose after a month, IBM (replace any company here) is ffering a different job chance from the one I applied previously, should I apply to this new one or I shouldn't as they already have my profile & CV? I don't want to destroy my repetition at those companies by applying again and again. Thanks.
Yes you should. They (meaning these large corporations) rarely actively do search in the resume database. Rather, the hiring manager and/or HR person more likely says, "who has sent me resumes for this job?" As your resume is already in the database it takes less effort to apply to future jobs.
You should reapply and aslo where applicable customize your resume/CV by putting the most relevant and best skills that is relevant to the position you are applying for. It is always better to stay away from one size fits all resume/CV. Also a one page cover letter illustarting why you would be the best person for the job (i.e. Matching your strengths & skills with the job specification) and your interst in working for IBM would be good.