Replacing curent image with GIMP Python plugin

I want to replace the current image opened in GIMP by another image using a Gimp-Python plugin. I was thinking of closing the first image and then opening the other but I don't know how to access the current image.

I was also stuck with a problem when i tried doing that. I have to call the plugin from a python file and when I try to run it multiple times in a row it only run the first time. Here is my code:

loadImage.py

#!/usr/bin/env python    

from gimpfu import *

def loadImage(file):
    image = pdb.gimp_file_load(file, file)
    gimp.Display(image)
    gimp.displays_flush


args = [(PF_STRING, 'file', 'GlobPattern', '*.*')]
register('loadImage',
         'Load an image',
         'Load an image',
         'Name',
         'Company',  
         '2015',
         '',
         '',
         args,
         [],
         loadImage)

main()  

main.py

from subprocess import *    
cmd = '(loadImage RUN-NONINTERACTIVE "/home/user/image.jpg")'    
#check_output(['/usr/bin/gimp', '-b', cmd])
call(['/usr/bin/gimp', '-b', cmd])  

This code just open an image in GIMP but I expect that it would open multiple images when I run it multiple times but it only open an image the first time. I tried with check_output() and with call() but it was the same result. I suppose it has to be with the batch mode but I'm not sure because i tried

call(['/usr/bin/gimp', '-b', cmd, '-b', cmd])  

and it would open two images.

What am I doing wrong? And is there a way access to the current image?