When it comes to trying to reach the Golden Age and such, I prefer the blurb in the Megaversal Builder that says travelers attempting to reach the Time of Chaos or anytime before get deflected into the future, parallel Earths, and other worlds due to the incredible temporal and dimensional disruption.
If you want an extra head-trip, and an idea of just HOW extreme the disruptions had been, consider the notion that large threads of pre-Cataclysm history didn't 'exist' as such
before the Cataclysm! That certain elements from the parallels around the world we would know as Rifts Earth were fully integrated retroactively into the world's history during it's alignment into a megaversal nexus. Does anyone remember where Kevin brought that up in?
In TMNT terms, imagine someone injected a high pressure line into the garden hose, increasing the TE pressure dramatically as well as straightening out the coils for
quite a distance. Enough force that the hose bulged and ripped so much that it nearly tore itself apart under the fury.
Continuing the analogy on a Megaversal scale, imagine all these various hoses floating about for the different dimensions, with parallels floating closest, with natural and artificial links and a few weak spots. Since TE only flows forward, the 'pull' of the high pressure stream at the Cataclysm created enough of a low pressure zone behind it to pull in some backwash through those connections. On the 'forward' side of the cataclysm, you have a great rush causing push and pull on the various connections and tears, along with swirling eddies, that continues at pressures normally seen much closer to the creation of some dimensions throughout the Time of Chaos. Even then, it's an oversimplification against the backdrop of all the spatial, dimensional, and mystical disruptions as well.
If using Transdimentional TMNT style, travel to there and before is impossible due to the straightening and realignment of the flows mucking up any attempts to go to previous Twists, fouling up any attempts to calculate correctly with J-scale forces of indeterminate beginning and end.
There are indications that time travel is possible on 'present' Rifts Earth, though. Particularly the two-way time holes to the future that occur in the Yucatan vortices, along with the usual rift, leyline storm, and triangle phenomenon. And there is still the 'hard way' of time-travel, but going against the flow is still an incredibly hard and slow process.
As for the effects of time travel, as far as I've been able to tell the Megaverse favors the single stream per dimension with the occasional related parallel dimensions nearby (whether these parallels are examples of parallel evolution or actually split for other flows at a point hasn't been covered directly). If you cause an effect in the past of your stream it will affect the same present that you are from. Though given Rifts Earth's relative instability, strong enough disruptions might cause 'natural' Patching and even
Twisting with the strong flows smoothing out minor disruption and
shearing off major obstructions. It may also be possible to prevent temporal changes from affecting yourself by hiding in a different timestream until all the changes have passed the time you want to be in, although you may run the risk of having to deal with a version of yourself native to the new timeline when you get there.
..perhaps I spend too much time studying trans-dimensional/temporal interactions. Then again, half the current group met over reading
Michio Kaku and the first thing I ever ran was a free-form trans-dimensional romp that grew out of 'What if' questions we entertained ourselves with.
Man, that brings back memories.. Now that I've distracted myself, I'll stop for a bit. I've probably missed going over something, but I'm sure someone will point it out.
Now
Buzz Off! I've got a Third Millennium to look after!