If you are allowed to renounce your Singapore citizenship without fulfilling NS duties, you may negatively impact your chances to work, study, or live in Singapore. Additionally, you may be disqualified from applying for a PR or citizenship in the future.
To renounce your Singapore citizenship, you must submit the complete contents and duly filled-out application forms included in the application package. Further instructions regarding the recipient and a list of documents are also included in the package.
You will not be fined or charged for cancelling your Singapore PR application. Instead, the ICA will send you a letter affirming your decision. After your PR status has been cancelled, you are still allowed to withdraw the lump sum of your CPF.
Singapore currently does not allow dual citizenship. If you want to be a citizen of a foreign country, then you must renounce your Singapore citizenship.