Rescript? No. You might have to convert the RPK for most engines, though.
2.3.0LE catalog SuperIDs
2.2.1 MWM catalog SuperIDs
Open up the RPK with Resdecode. You can edit the RDB files that Resdecode produces (with Notepad or something), but you cannot open RPK files directly. Look for every SuperID on the LE list (in "class" or "cfg" entries). Replace them with the appropriate MWM SuperIDs. Then use Resconvert to change the RDB file back to an RPK.
For example: (This is from my Fiero.)
<FILE 00000023.res >
typeof 8
superid 0x0002AD5C
typeid 0x00000001
alias GM_L44_2_8_engine_block
isparentcompatible 1.00
</FILE>
<FILE 00000023.rsd >
script parts\engines\General_Motors_L44\scripts\GM_L44_2_8_engine_block.class
native part parts\engines\General_Motors_L44\scripts\GM_L44_2_8_engine_block.cfg
lod_amp 4.000
</FILE>
This ID is 0x0002AD5C, or just AD5C. In LE, this corresponds to "V6 Engine Blocks". You will want to replace it with the MWM "Engine Blocks" ID. If you look at the charts I linked to, the correct one is 0x0002025C.
<FILE 00000023.res >
typeof 8
superid 0x0002025C
typeid 0x00000001
alias GM_L44_2_8_engine_block
isparentcompatible 1.00
</FILE>
<FILE 00000023.rsd >
script parts\engines\General_Motors_L44\scripts\GM_L44_2_8_engine_block.class
native part parts\engines\General_Motors_L44\scripts\GM_L44_2_8_engine_block.cfg
lod_amp 4.000
</FILE>
Once you have done this for every part, you can re-convert the RPK and paste it back into your game installation.
Note: The first four digits of the SuperIDs will be 0x0004 for cars and 0x0002 for engines!
I hope this is helpful. If not, please reply again.