It might be cheaper overall to get someone in to run another cable & terminate it. The chances of successfully crimping on another RJ45 connector to a pre-made lead are slim, even if you have the correct crimp tool.
Do-able if the correct plugs are used. Solid core and stranded plugs are different.
You are right, however, its fiddly at best. Doing it with failing eye-sight? Well, good luck with that.