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1) Imagecrafter doesn't say "in addition to its other types", so it overwrites all creature types the creature previously had.

Edit: In case you need rules support:

205.1a Some effects set an object’s card type. In such cases, the new card type(s) replaces any existing card types. Counters, effects, and damage marked on the object remain with it, even if they are meaningless to the new card type. Similarly, when an effect sets one or more of an object’s subtypes, the new subtype(s) replaces any existing subtypes from the appropriate set (creature types, land types, artifact types, enchantment types, planeswalker types, or spell types). If an object’s card type is removed, the subtypes correlated with that card type will remain if they are also the subtypes of a card type the object currently has; otherwise, they are also removed for the entire time the object’s card type is removed. Removing an object’s subtype doesn’t affect its card types at all.

205.1b Some effects change an object’s card type, supertype, or subtype but specify that the object retains a prior card type, supertype, or subtype. In such cases, all the object’s prior card types, supertypes, and subtypes are retained. This rule applies to effects that use the phrase “in addition to its types” or that state that something is "still a [type, supertype, or subtype]." Some effects state that an object becomes an “artifact creature”; these effects also allow the object to retain all of its prior card types and subtypes.


2) Not at the same time, but it is possible to block and then tap/sacrifice the blocking creature before combat damage, as long as there is something allowing you to. If the blocker doesn't exist anymore, the blocked creature will remain blocked and will deal no combat damage to the player/planeswalker it's attacking unless it has trample or a similar ability.