Chrome Flesh pg 146, Nanoware Ratings and Degradation
All nanoware has a Rating that represents that specific nanite colony’s hardiness, versatility, and level of performance ... the Ratings of nanoware systems permanently degrade over time, at the rate of 1 Rating point per week. A functioning nanohive (p. 151) counters this nanite loss by providing a safe environment for replenishing feedstocks and colony numbers—regardless of whether the system involves hard or soft machines.
Chrome Flesh pg 151, Nanohive
When the nanoware supported by a nanohive has its Rating reduced, the nanohive returns its Rating by 1 point per week, up to the nanohive’s Rating.
Each nanohive supports one nanoware system at a Rating equal to its own.
Hard nanohives can ... reprogram the nanite system it supports—its Rating is the number of different hard nanite systems to which it can convert its nanites.
Now...
The way I'm reading that, Soft Nanohives have a Rating which measures how high the single Colony rating it can support. So a R4 Soft Nanohive can support a single R4 Colony. If you purchased a R5 Colony, it would start to degrade, and the R4 Nanohive would only bring it back up to R4, meaning you wasted some money in the long run.
Hard Nanohives work the same way, supporting a single Colony at their Rating. However, they can also store Rating's worth of programs to change that colony to do something else. So an R4 Hard Nanohive can support a single R4 Colony, but it can program that Colony to do 4 different things. The Colony can only do one thing at a time, but there are 4 options to choose from.
So...
You could purchase a single R4 Hard Nanohive, and a copy of Anti-Rad, Control Rig Booster, Implant Medic, and Nanite Hunter. Then you decide what you want them doing most of the time. But later on, you can change to another of those 4 choices if you want. I'm not seeing anything in the book that says you can or cannot swap out the software in the Nanohive later on. But since it already stipulates a limit of 4 stored, and only 1 running, then I'm inclined to think you need to choose the 4 programs from the start and you're stuck with those choices. Otherwise you could swap them out all the time, and there's no point to saying "only 4".
If you wanted Anti-Tox, and Carcerand-Plus, and Nanosymbiotes... you would need to purchase 3x separate Soft Nanohives. Each one would be factory set for that single function, and could not be changed.