A skilled programmer

what I am trying to do is alter the length of a time series. For instance if a time series is 10 weeks long I want to have the ability to make it 13 weeks in which the y axis values is distributed evenly based on the new time scale. Its kind of like shrinking or expanding a picture horizontaly. But I want the new data exported on a csv file with the same format as the input. The second thing I need is to use several edited time series in the way above and join them together. The way i want them to join is by giving the final value of the primary time series to the beginning of the second time series and have the percentage gain in the second time series be used to determine new values for the combined time series Let us say that the first time series ends at 13. The second time series starts at 26. We will make the first value of the second time series as 13 and use the percentage difference between each successive data point in the second time series as a basis to either add or subtract from 13