Is it feasible to raise wages and then appeal again?

It will attract more attention, unless backed by a strong justification as to why the raise.

There are two aspects to this question:
1. The employer must stay within the salary range given in the (locals only) jobs bank posting to hire a foreigner (you) for the job. If they want to raise your offered salary above that range, they'll have to post it on the jobs bank again (for a month) with an increased range and can only hire you if still no suitable local applicant is found.
2. Re-applying with increased pay often comes with illegal kick-back schemes (i.e. the increase does not really exist and the applicant has to return the difference to the employer), thus MoM will scrutinize such cases in more detail. But if your employer has a convincing explanation why you are suddenly worth more to them, there is no harm trying.
Remark: S$6000 seems very low to me for an MBA holder with six years applicable experience. Did you check what the SAT tool says for your case?

thanks for your help.
1. The raised salary increase is still within the range
2. I checked with SAT and the result showed that I was qualified.

From my experience, 6k is a bit low for your qualifications. I recently got rejected with 6k while having 1 year exp and a bachelor degree (internship at an investment bank). SAT does not apply to financial services firms, as you can see from the disclaimer on the website.

Apart from salary, I think it has been very difficult to get an EP if you are working in finance these days.