Since the concentration of your stock solution is 1000 mg/ml , if you take an aliquot of 10 ul, the concentration of the solution remains same unless you further dilute to a certain volume. But the content in 10 ul will be 10 mg only.
An aliquot volume has the same concentration as its original solution. So it is still 1000mg/l and may change only by dilution or concentration process. However, if you are accounting uncertainty propagation, then the confidence interval may change due to the contribution of your aliquot volume errors or pipet ones