This scenario is dedicated for those who already have a running masternode controlled by Dash Core software wallet and who are willing to move its management to a higher level of security provided by hardware wallets.
In the old configuration Dash Core controls the private key of the 1000 Dash collateral and is used to send start masternode command. In contrast, in the target configuration, 1000 Dash collateral is controlled by a hardware wallet (like Trezor) but the start masternode command is invoked by DashMasternodeTool application.
The procedure described below boils down to sending 1000 Dash funds from your Dash Core wallet to a new address controlled by a hardware wallet and setting up a masternode configuration in the DMT. You will not be changing any of the dashd configuration parameters, so you will not need to restart it at the end of the sequence. You must be aware though, that sending a start masternode message will reset the masternode's location in the payment queue. For this reason, the best moment for this type of reconfiguration is when you receive your last payment.
Each of the hardware wallet types has its own native client app for performing transactions - in the following steps I will not cover all of them, but instead I'll use Trezor and his native WEB aplication as an example.
Open Trezor's native wallet in Chrome browser: https://wallet.trezor.io, enter your pin/passphrase if enabled (I strongly recommend enabling both).
Use the first empty account and dedicate it for your masternode. If you don't separate your daily accounts from your masternode account, then you may have a problem maintaining your 1000 Dash transaction intact and this will end up with kicking your node off from masternodes list. The reason is that the wallet.trezor.io does not have a coin control feature which allows blocking certain transactions from being used when making day-to-day operations.
This is your new masternode collateral address.
Open Dash Core wallet and send exactly 1000 Dash to your collateral address.
Click the Tools->Open Masternode Configuration File menu item in the Dash Core. This will open the masternode.conf file in your default text editor. This file contains your existing masternode configuration of which parts will be used in your target configuration.
Each masternode entry occupies one line as shown in the screenshot below (the line is wrapped):
Each line consists of five to six sections (in the screenshot surrounded by green/red rectangles):
A. masternode name
B. masternode IP:port
C. masternode private key
D. 1000 Dash transaction id
E. 1000 Dash transaction index
F. masternode's collateral address (not mandatory)
Only the first three - labeled as A, B and C - will be reused in the target configuration.
Run the DashMasternodeTool application and click the New button to enter into the new masternode mode. If you don't have any masternode entries in the current configuration, the new masternode mode is activated automatically.
Copy the name (you can change it - it's just a label), the IP:port and the private key to the corresponding fields in the DMT.
Enter your collateral addres obtained in the Step 2 into the Collateral edit box, then click the little tiny botton on its right (with the icon of the right arrow on it) to retrieve the BIP32 path related to the collateral address.
To fill in the id/index of your 1000 Dash transaction (which you have sent in Step 3) click on the Lookup button. Assuming that transaction has been processed without any problems, one transaction should appear in the dialog that will show up:
Select the transaction and click OK.
You should see the Collateral TX ID and TX index fields filled with the relevant data:
Click the Save configuration button.
Before you go to the last step of the whole configuration (sending start masternode message), make sure that the number of confirmations of the collateral transaction is greater or equal to 15 (this can be verified in the Lookup dialog). Without this, starting masternode will not be successful. When fulfilling this requirement, you can go on and perform the start masternode operation.