Solution
It is possible to change datatype of stored data when you use MDF4 Dataplugin. See the following snippet. You can implement this snippet into your vi.

Note: This image is a LabVIEW snippet, which includes LabVIEW code that you can reuse in your project. To use a snippet, right-click the image, save it to your computer, and drag the file onto your LabVIEW block diagram.
In order to change data type, you should
- Set additional parameters as <nativedatatype>true</nativedatatype>
- Set available Value.
Each value represents different datatype. Please refer to the following table.
| Value | Datatype |
| 1 | U8 |
| 2 | I16 |
| 3 | I32 |
| 4 | I64 |
| 5 | R32 (double) |
| 6 | R64 (long) |
| 7 | Time |
| 8 | String |
| 11 | U64 |
| 12 | U32 |
| 13 | U16 |
| 14 | I8 |