Yes. VT Markets offers this service.

If you want to do this on your PC MT4 / MT5, the process will be as follows:
1. Go to the "Trade" page, whose button is at the left bottom corner.
2. Right-click on order you want partially close
3. Select "Modify or Delete the Order."
4. Change the type to "Market Execution."
5. Set the lots you want to close
6. Click on the "Close #order number...." button

If you want to do this on your MT4/ MT5 App, the process will be like as follows:
1. Visit the "Trade" at the bottom list
2. Click on the position you want to partially close and long-press it again
3. Select "Close."
4. Set the lots you want to close
5. Click "Close with ..."

If you want to do this on VT Markets App, the process will be as follows:
1. Visit the "Order" page by clicking the button at the bottom list
2. Go to the "Open Positions" section
3. Click on the position you want to partially close
4. Select "Closed."
5. Set the lots you want to close
6. Press the "Confirm" button.