Long story short my magus has to erase some of his memories to ensure that a tribunal investigation will find no suspitious detailes. My problem has two parts:
What kind of spells to use? (Possibly 1-2 magnitude)
How to construct a believable, authentic mental environment for yourself?
What do you think how is it possible to erase/edit your own memories in a way that is not suspicious for the inspector/quesitor, and is only mindly suspicious even for yourself? Bc the best platform of a good lie is when you think you tell the truth!
How can someone mislead himself to construct a coherent new story about what happened instead of knowing the dangerous truth?
How much memory needs to be hidden? Also, do you have a Familiar? enchant the familiar bond so that the Familar can hide your memories?
It might help to have a history of magically going into you mind, in case the Q gets permission to look inside.
InMe to recall faded memories, CrMe to enjoy your favourite emotion should all leave valid casting sigil traces to obscure what went on in there.
This spell is given in a box, top left corner of page 120 of Legends of Hermes.
It is of the 1st magnitude, but does not (directly) assist in forging a false memory - that would be CrMe and a lot harder.
PeMe to destroy your own memories is relatively easy, as has been indicated already. There are other ways to manage this but they are all more difficult. Though they may have the advantage of preserving your original memories for yourself.
There are canon spells which deceive truth detection spells for example. The most common interrogation technique typically is the "Frosty Breath of the Spoken Lie" spell, both because it is explicit/visible to everyone involved and because (usually) people aren't left with it being unclear if anything "else" was done in someones mind when they submitted. Q's are not without their own interests as individual Magi after all.
I did have an idea for directly providing deceptive feedback to a mental divination such as "posing the silent question" for example, based on the CrVi magical shell guidelines.
CrVi (General) (Create a magical shell which gives false information about the target to Intellego spells with level less than half its (level plus one magnitude).
Directly by itself this seems like it could deceive a variety of Intellego magic, depending on how the shell is viewed and constructed. There is also the intriguing possibility for adding requisites. What if a Mentem requisite is added to the shell?
I had toyed with the idea that this would create a magical shell layer inside the mind of the target that could contain false memories, and then once created this layer and the false memories it contained could be manipulated either with Mentem or perhaps Art of Memory.