We sought this protocol to learn how to do intradermal inoculation...

I completely agree that the intradermal inoculation is challenging and requires regular practice. A key challenge I found was that the ear may have several punctures after a few attempts, leading to leakage of the inoculated solution. Decreasing the injection volume to 5-10 µl may help.
A colleague follows a similar protocol by attaching the ear skin to a double-sided, sticky tape for the injection (not requiring forceps). Despite potentially being easier, the subsequent "tape stripping" may induce dendritic cell migration, which was a key readout for us.
Alternatively, one could inoculate the dorsal skin of the mouse back intradermally. Nevertheless, this procedure requires shaving and dehairing of the skin, which also induces irritation and does not guarantee steady-state conditions prior to inoculation.
For these reasons, we decided to perform the procedure as described in the protocol.