Just edit your segments and then produce each one separately with a file name, eg myfilm1 and so on and save them in a directory. PD will place them in a default directory called PD projects.

When you have completed the segments open a new project in PD and import your myfilm clips from the directory they were saved to. Place them on the timeline in the correct order and then produce it again as a new much longer film. Of course you can still insert transitions between the clips as required.

Good luck with it Panny TM10, GH2, GH4,

I recently did it this way. It's time consuming but worked.
I scrolled along the time line to predetermined time slots and split the video into the requisite number of segments.
Then I selected each one in turn and saved them to my temporary folder as title 01-02 etc.
Then I opened each one as a separate project edited to my hearts content.
Then placed the first one on the timeline scrolled to the end and inserted no 2 and so on until I had them all in place.
Then ran a few checks to make sure all was well. Saved the project.
I had to split the whole into three Chapters in order to fit it to DVDs.
It actually seems to have taken longer to explain now than it did to do the project.

The way I do, first make sure I SVRT that will connect a compatible profile.
Split the long video in two or more pieces, selected with yellow sliding, the first part, Produce Range button to save profile obtained with SVRT, quick process (not the video rendering) saved video part 1.
Repeat to part 2 and 3.
Now edit Part 1 Project 1 save, edit, Part 2, Save Project 2, edit part 3, Save Project 3.
To save video 3 projects at once.
Open Project, Project 3,
Insert Project, Project 2
Insert Project, Project 1
Note the seams between 1,2,3 is needed transition.
Next to Produce, save to video file of your choice. AMD-FX 8350 / 8GB DDR3
SSD SUV400S37240G / 2-HD WD 1TB
AMD Radeon R9 270 / AOC M2470SWD
Windows 7-64 / PD16 Ultimate