Is it possibke to generate the random words of a SLIP39 Seed and let the Trezor generate the checksums?
When yes: It is possible with all Seeds or only with 20 word SLIP39?
Trezor has no such feature.
Nothing stopping you from doing it by hand though. Calculating the checksum by hand is much easier for SLIP39 than for BIP39: it’s just a couple bitshifts and XORs, times the number of words (17 for a 20-word seed).
Someone could even create a worksheet for this: precompute the customization string on computer, pre-convert the constants to bits, and make a checklist “if bit X is set then xor this constant”