I have a SRAM 8 speed chain that's pretty new that I need to remove and reinstall on the bike. I don't know if disconnecting and reconnecting the master link is a good idea. Any reason I can't do things the way I did back in the eighties and nineties? Have modern chains changed?
A long time ago, I bought some SRAM 8 speed chains too. The reason I did so was that I found some old brochure about the connecting methods, and they specified chain tool as one possible connection method (with quick links being the recommended connection method). The brochure had a model of a chain that was still sold although the brochure was few years old.
Since I don't like quick links, I threw the quick link away. I connected the chain with a chain tool. Then, when just pedaling along, the chain suddenly snapped. I had a chain tool in my emergency tool kit so I just reconnected it, thinking that I must have done a poor job in connecting the chain. Then some time later, the chain again snapped. I had to reconnect it again.
After this, I carefully investigated the chain. I noticed that the chain pins were punched. So the press fit between the chain sideplates and the chain pins is not strong enough. The chain pin is pushed to the chain sideplate and a machine punches it at both ends to improve retention.
If you push a chain pin of this type through the sideplate, both the punching at the end of the chain pin, and also the sideplate hole, will be damaged. When reconnecting, these damaged parts do not have a secure press fit.
A new SRAM brochure no longer listed chain tool as an allowed connecting method. So what must have happened is that SRAM changed its manufacturing method to have poor press fit and improve the retention by punching the pins, without changing the model name of the chain that was sold.
This caused me to switch to Shimano chains and never look back. The Shimano special reinforced connecting pin can be pushed to side plates that have been damaged by pushing a punched chain pin through them, costs some extra, and does not allow using the same connecting point again so you must be sure to break the chain again at a different point. However, the Shimano special reinforced connecting pins are cheaper than quick links, weigh less than quick links (important for keeping your emergency toolkit weight down since ideally you will be carrying not one but few of these), and are very easy to install, far easier than installing a standard chain pin. The benefits outweight the drawbacks: most chains see very few if any removals in their lifetime so the extra costs are not an issue (these stupid bushingless chains last so little with proper care anyway and are cheap so it's not worth the time and effort to clean them properly off the bike), and the maximum amount of times you can reconnect a single chain is equal to its link count, usually 116. I don't think any chain will be removed more than 116 times in its lifetime.
At least the Shimano still sells chains that allow not using these stupid quick links.
So, the short answer to your question is: YES, modern chains have changed, and NO, you cannot use the old chain connecting methods anymore. But with Shimano you can use these special reinforced connecting pins with a standard chain tool.
There may be some benefits of the punched pins. They allow shifting when under load. On a non electric bike, an experienced cyclist does not do that, but the response time of electric bike motors is not so fast that shifting without any load would be feasible on electric bikes. About the only way electric bikes would allow shifting not under load is electric shifting -- standard mechanical shifters are not connected to the motor computer, so the motor computer doesn't know when you are about to shift and cannot reduce its electric assist in advance to anticipate the shifting.