A reference to the use of explosive bolts for emergency jettisoning of the rocket tubes has circulated through a number of books. However, I've never found anything other than a vague statement about its existence. There is no concrete evidence on this that I have found or it would be easy, but here is the circumstantional evidence that I base my opinion on:
Was this just part of the plans for the weapon system that never actually found much use in the field, or was it actively used? It's fairly common for authors to find plans in their research that differs from what actually made it into use. Was it used in all aircraft that mounted the weapon system? If it was actively used to jettison tubes after firing, it would be counter to all anectdotal evidence on the matter that I've seen. Given that performance degradation is universally cited as a downside to this weapon system, isn't it odd that its never mentioned that the aircraft is completely free of this after the weapon is fired? 21cm rocket installation was not a factory mod, but rather a field mod. The installation of explosive bolts to jettison the tube might be a grand idea, but one that may be impractical due to problems in supply and maintenance.
The reference to such a system do cite it as being an emergency jettison, and if such a system was in place operationally, I do believe that is all it was used for. I would say that the emergency it was designed for was one of the nature of losing your engine on takeoff and needing to rid yourself of extra weight and explosive ordnance before you ditch rather than just cleaning up your airframe after you fire them off. The latter case is all it would be used for in AH and is why some people want it.
If the system was designed to be jettisoned after firing as a matter of procedure, why would explosive bolts be chosen as the means to accomplish that criteria? Can anybody name me another ordnance system that was designed to be dropped that used explosive bolts as the release mechanism? Does that really sound practical, especially in a situation where multiple sorties were flown daily and quick turnarounds were a necessity?