Rewriting some texts of a 270 years old handwritten document - that's a difficult task for a beginner if the result must look authentic in a high resolution photo. But if you fight your way through it succesfully, nobody will say you a beginner.
You need no special equipment, only paper and a suitable pen for this style- maybe a quill or one with steel nib. And a good camera + the skills to take a fitting photo.
In addition you need a massive amount of serious practicing to learn to write in the same way. It's well possible you will never develop the needed penmanship to write plausible replacement texts. The original writer can have practiced for ex. 20 years. It was his job.
If you are lucky you can find elsewhere from the same book usable snippets. If you place them to a new layer, someone can get fooled. Seamless insertion is complex. You must fit also those texts which are faintly seen through the paper.
If one had a piece of dark paper behind the photographed page, the backside could be faded from the image.
If you plan to rewrite a part of the texts in a computer, do not expect any existing computer font do the job. A genius is needed to program one for you.
My suggestion: Check, if rewriting whole spread or page is acceptable. Then you have a bigger possiblity to get it done with consistent style. If you cannot lift your handwriting ability to a plausible level, you possibly can find one with the needed skills.
If the book isn't the main subject in the work, rewriting all texts with a rich enough computer font can be acceptable. The task is still complex because manipulating the text to seem to be handwritten onto curved, partially transparent pages is a must. But that's another technical problem.