Reset the meter/create a break in the middle of a track?

Is there any way that I can create a break in the track at a given point?  (Almost like a page break on a word document.)  Leaving an incomplete measure?
 
I'm doing some scoring and want to nail a transition with a sequence, but I don't want to mess up everything that has come before it.  To get around this, I've been creating separate projects for each part and then merging them in yet another 'final' project.  That method was fine for a longer movie, but for a 60 second trailer - it's really inconvenient.  
 
Any suggestions?

I don't think I'm asking the right questions... :)
 
Here's an example.  For the first 30 seconds, I want to play something that is 100bpm.  At about a minute, there is a transition and then I want to crank it up to 120.  But I want the first beat of the new tempo to sync with the images.  So, if I could just cut off half a beat of the last measure, I could do what you suggested and just change the tempo.  But I think there is probably a different technique I could use to accomplish this...  
 
The searches I've been doing lead me to believe it's something about "set beat/measure to now" but the problem I'm running into is that it's changing the tempo of all the previous material.
 
Any suggestions?

Gotcha...  That might work, but it would still be hard to get it to sync up to that exact frame.  Feels like a workaround to me.  What I've been doing since posting this question is creating a new tempo a fraction of a second before the transition frame, the setting the Now marker at the frame and clicking project->set beat/measure at now.  Then it appears that it adjusts the tempo after the last switch and before the new beat measure.  It switches that tempo to something insane like 423, but it doesn't mess with everything before it.  The only problem is that it does effect all my markers...
 
It seems to me that there is probably some "pro" technique that I'm missing here...  Or am I?  Maybe the Pros just have a variety of workarounds to pull out in different situations?

I'm not sure if anyone is still reading this, but I figured I'd add that I've been using "fit to time" a lot more.  I can highlight a long section right before the big emphasis and the click "fit to time" - as long as I click Tempo Map - it adjusts the tempo ever so slightly and matches everything up...  Works great most of the time.  On a few occasions I've had difficulty and I'm starting to think there might be a bug in the system...  I'll have to do some more editing to rule out my wrong doing first, but on one occasion it changed all the midi events.  Even "undoing" didn't correct the problem - I had to close out the program and redo from the last save...