If you can not overwrite manufacturer data (e.g. manufacturer name, s/n etc.) then transceiver is write protected. If you can overwrite this data - it's unprotected.
To unprotect it, it may be required manufacturer password (in most cases), but it can be protected also with other method (which is known only by manufacturer).
Manufacturer entry password for SFP is usually located in addr A2h 7Bh - but there are some transceivers where location of password is changed, e.g. A2h FCh. When you used brute force for whole range for A2 7B and it not found anything, you can check to run brute force on A2 FC (first only on ASCII chars - it will be faster, then on whole range). If it still not find password it means that it has to be protected on other way or password is stored in not usual place.
You can try to get some information from manufacturer (10Gtek in your case) who knows, maybe they will share it to you.