我想問..如果我已經18歲..但只有臨時身份證..未有得羅真正個張身份證..可唔可以開到銀行戶口?

Yes.
As the document is issued by Immigration Department. The details of it, particularly the ID card no., will not be changed. However, the bank may require you to give them an inspcetion of the new ID card later and get a photocopy of it for bank's record.

臨時身份証是不可以開銀行戶口的,因銀行要正本身份証存檔.