Can I put an access hatch in the front cabin or bonnet?

In most cases it’s a matter of just cutting it in and adjusting the structure around it a little. It is best to run your plan past the DBA, so it can be checked that it doesn’t upset the structural integrity of the area. DBA may come back and suggest adding a extra piece of structure.

And the stately ships go on
To their haven under the hill;
But O for the touch of a vanished hand,
And the sound of a voice that is still!

Alfred, Lord Tennyson