The trick there is to make your own dummy pin which is of the same diameter as the one that locks the trigger block to the compression tube. Make sure that the length of the dummy pin is just enough to clear the thickness of the compression or else you can't slide the trigger block away easily. What I meant by that is that the dummy pin should be of the same length as the diameter of the trigger block housing (or tinny, winny, smaller than the I.D. of the compression tube). Without this jig it would take you a lot of time and effort to disassemble and assemble them. I'll see if I can make a picture of it.
With regards to the double trigger blade of the RM Mendoza airguns it is one of the simplest and ingenious type of pseudo 2-stage triggers available. Just take off the pins and don't worry if the small springs fall off. The trick here again is to glue the tension springs of the 2 trigger blades to the trigger blade holes itself (I use superglue but just a very small amount). Just a small amount to let it dry and make a hard cement on the spring and the trigger blade. Now, when you insert them back (the trigger blades) to the trigger block they will keep their location and you can just use a precision long nose pliers to insert the other end of the tension springs to the safety mechanism part of the trigger block. If you have done this it will only take you less than 15 minutes to fully assemble the trigger assembly to the tube and fully assemble your airgun in about 10 minutes.
