Is it dificult to adjust the handbrake of a Nissan X-Train model 2004?

You may need new hardware rebuild kit or its also a sign that the rear shoes need replacing. I would pull the drums off and confirm which it is you need or if anything is missing. I like to buy the Parking Brake Rebuild Kit when changing out rear brakes ans using alot of brake Cleaner and if the drum is thin or grooved bad or if they were let go until metal to metal just change them out too. The rebuild kit does not come with every single item that can be removed while doing this repair Like the wheel cylinders the arm that goes between the upper part of shoes that hold it all tight and is vital to e-brake function so look at its condition and the little washer & spring on it on one side has to be put back together correctly and in good condition, the kit does come with that spring though but not the washer/plate or forked arm. If you need shoes its best to replace the hardware in the kit anyway and vice-versa if replacing the hardware replace the shoes. and the E-brake will be just fine, the full rebuild kit comes with the adjuster too, so get the full kit and apply some good lube oil (like Fishing reel oil or gun oil or ATV wire cable lube or any light oil for automotive use) to adjuster threads before mounting it up to (not sopping wet though wipe off excess) make sure if functions as intended. If the one you have are gunked up and not working good this one fix can keep them working, just clean well before hand and adjust the shoes out far enough that you could not adjust out any farther and still get the drum on., then when done back up slowly a few times to set the shoes in the proper placement. After this the e-brake will work like new.

Also if putting on new drums remember they come with some light oil to keep them from rusting while on the shelf so clean off with soapy water minutes before putting them on or use the brake parts cleaner so it will be dry enough to use right then..

Get a phone or digital camera and take shot from all direction to look back at while doing the rear brake rebuild, and lay out all the new parts like they be when mounted and as you take it apart lay the old parts by the new parts and buy a rear brake spring tool kit, they are cheap and worth not breaking fingers and elbows. Watch some youtube videos.

I look at both sides to compare if they have been installed correctly also before taking apart by using a diagram from the repair manual as I have seen them all messed up. Each part goes on in the same location but when you turn around and face the other side some people get confused because now everything you just put on the other side is toward your other side. I trained myself to think of it as not which side I am facing but which is the back shoe verses the front shoe and how everything goes together that way, and the way the adjuster faces no matter the side your on, one side of it always goes toward the front of the car and so forth with the other parts. Some springs go on first. I like to assemble the bottom parts first then slightly turn the shoes to an angle and place in correct position get my shoe springs installed put the e-brake arm in and its spring and washer and make sure its all squared and put my first upper spring in while making sure the groove in wheel cylinders are aligned with the groove in shoes then just before putting spring in I pull the e-brake cable up and mount then the spring and keeping it from shifting I put on the other spring on. Its easier that way for me but if new to it can be a house of cards. But some of those other ways of doing can damage springs or have them at bad angles ect if not done with care. I know I did not give 100% accurate details there but you get the idea. Its easier to get the bottom springs in for me by doing the bottom side first then doing the balancing act to get it in place and all the upper side completed without stopping until its all done but then again if you watched me you would say what the heck did you just do I missed all that. When I assemble I assemble. Like hold holding five baseballs in one hand you always miss how they done it until you realize they are holding 5 baseballs in one hand.