I don't think that property setting elements, or elements that run console commands, are a good idea.
1. It means that saves rely on the exact details of how elements are implemented, which makes it a lot harder to change things or tidy up the code without breaking saves.
For example: merging all life elements into one and reusing the element IDs. If an element that could set ctype had existed, any saves that used it to set clone to produce a particular life element would have been broken.
2. If you change any particle properties except through normal element interactions (e.g. by using the console or a property setting element), you do so at your own risk. The game may crash, or elements may not work as they are intended to. I try to make elements do sensible things when people clobber them with the console, but loads of them still don't behave well when fiddled with. Mostly, I haven't bothered fixing any strange effects that don't survive being saved. Console commands in saves would be opening a whole new can of worms.
If you can only make it using the console (molten stkm, frozen sing, bomb powder etc), don't be surprised if it stops working at some point in the future, and don't rely on it doing anything predictable. The only things you can expect to work in the future are things achievable through normal element interactions (and even then, changes are sometimes made if there is a good enough reason to do so).
I would prefer not to see saves relying on things that might not work in the future. People complain when things break.
Converting it when loading an old save: true, but that only works if the property setting particle can only affect one element (i.e. no "!set ctype all aaaa"), which isn't the case for the original suggestion in this thread and many of the previous property setting particle suggestions.
Because if a property setting element sets the ctype of all elements, you can't just change the value it sets the ctype to (e.g. changing the value from BRAN to LIFE) to make clone work when element numbers change. Different particles use ctype for different things, it doesn't necessarily refer to an element.
I was wondering, why can't we say !set type metl lot? We can only do LIFE and it doesn't make sense for me. Like there's a trick when you place DMND change it to PHOT while paused and give it 0 life then say !set ctype phot life and it's stationary and Blue. Plus it has strange conduction capabilities. Same can be done with ELEC and NEUT (NEUT, not so well.)