How to stop Filezilla changing the linebreaks

What is the line? You can just have arguments on the next line without any problems:

a = dostuff(blahblah1, blahblah2, blahblah3, blahblah4, blahblah5, 
            blahblah6, blahblah7)

Otherwise you can do something like this:

if (a == True and
    b == False):

or with explicit line break:

if a == True and \
   b == False:

Check the style guide for more information.

Using parentheses, your example can be written over multiple lines:

a = ('1' + '2' + '3' +
    '4' + '5')

The same effect can be obtained using explicit line break:

a = '1' + '2' + '3' + \
    '4' + '5'

Note that the style guide says that using the implicit continuation with parentheses is preferred, but in this particular case just adding parentheses around your expression is probably the wrong way to go.

To pause the transfer and complete it later:

First of all, before pausing make sure to go to the "Failed transfers" tab in the queue box and right click it then click "Reset and requeue all".

After that you've to go to the "Queued files" tab and right click the queue box then uncheck the box "Process Queue" - by that you've paused the transfer, you can close FileZilla and complete it later.

How to resume? Just right click the queue box again and check the box "Process Queue".