Sorry for the delay in responding to various comments! A bit hectic with the pandemic.
"I'm not sure I would want the Hurling line of spells to be instantaneous though. Hurling can be quite a powerful effect -- if I understand it correctly, a Hurling II spell could hurl a two-handed weapon, and attack on the weapon's chart with the caster's Directed Spell OB? That seems like the type of spell that should not be instantaneous, or else one could get a full melee attack and a full (instant) spell attack in the same round (in RMU at least)."
First, all Mentalist spells in BASiL are instantaneous, but that is easily changed by the GM. (This isn't explained in the spell lists--but will be in the final version of d100 BASiL.). Second, yes, the spell attacks on the appropriate weapon chart using the directed spell bonus. I see no logical fallacies with this.
"as written you can use Hurling to disarm a foe (they get an RR) and then if the RR is failed attack them with it, all as the same instantaneous action. That does seem a bit much. I think it would be ok as a base list for a pure caster, since you normally only get one spell per round and they are not going to be great at melee, but these lists are intended to be more general than that. Compare to shock bolt, which is the same level on a base list, not instant, can't disarm (but does have better range of 100' vs 50' here)."
I have no problem with a spell having a tertiary effect. (ie the spell hurling may also create a disarm effect). For instance a Fire Bolt or Fire Ball should have a substantial effect on worn equipment and/or breakage. Other spells might have an effect on fatigue. If the issue is with it's instantaneous effects, I allow all Mentalism spells to be instantaneous. They have MANY other limitations. If it's being compared to RM, BASiL is an easy improvement, if it's comparison to RMU it's irrelevant. I posted all of Essence and Channeling around the same time as RMU Spell Law Beta1 came out. I'm not sure picking out one or two "issues" makes for relevant criticism--this is meant to be amateur submissions just like other proposals in Guild Companion, Rolemaster Ring or all other online fan sites and similar contributors.
"I like the liquify spells distinguishing liquification from melting. It's physics-defying which feels properly magical. It leaves a lot to the GM to decide for the organic one, though. If you liquify a tree and pour it into a mold and solidify it, do you get an item that is structurally wood (with grain, burls, etc) or has it just become some kind of organic plastic? I like the former interpretation better myself."
You touch upon a significant issue: spell effect descriptions. If they are too open, it allows for broad interpretation. If they are too specific, they seem to "physics" and lack a magical wonder that appeals to you. I have no answer to you for that. Interpret based on your setting--we had to do that even in the original RM.
"Might be good to add some spells for detecting projections and banishing them back to their bodies or even attack and trap them (at high levels) or some way to project yourself and/or others so you can fight other projections. That would also be a good way to balance the power of otherwise undetectable scouts."
Counter spells or detecting spells should be contained in another spell list. Otherwise you have cancelling abilities between the same type of casters and lack of specialization. I prefer the idea of specialized abilities and specialized counter-abilities.
"is this not covered by dispel/cancel/sense/detect Mentalism ?"
Yes.While I removed the realm specificity for detecting, cancelling and countering, those types of spells would be applicable--again depending on the setting.
"yes i know this depends upon world style, imho the dispel will either attack the
spell link/matrix or thread (Earthdown style)
arcane connection (Ars Magica style)
silver cord ? (OOBE style)"
Yes! Let's be honest. RM spells are sort of setting specific but create a lot of problems in specific settings. This is good analysis!