Hi Agacija,
The simple answer is no. There is no tool that merges two res11 files and generates only one file with the content of both files (as far as I know). But, there is a more complex answer , too. You have two options, depending on the context:
1. As Craiggoo said, you can load both files in Mike View and make some plots an so on using information from both files.
2. You can add results of your simulation to an existing result file. This can be done by open the Simulation (*.sim11) file, go to "Simulation" tab, at the section "Initial Condition", for HD model select "Hotstart" as "Type of Condition" (the same for the modules AD, ST, RR). Now, you can select an existing RES11 file (in your case, the file which contains results from 2000 to 2008) and check the checkbox button "Add to file". At this point, you can run the simulation for the next period (2009-2016). As you may observe, this solution is possible only if you have the model and data to run again the second period. Also, you may want to have a continuous time axis for your results, so the two periods should be right next to each other.
Regards,
Aurelian