My car has a Aisin 81-40LE(Toyota U440e) 4-Speed Automatic Transmission. I want to change ATF, can i use multi-Vehicle ATF's like "Aisin ATF Plus"? Also can i mix new fluid with old? Can we use Multi-Vehicle Automatic Transmission Fluid (ATF) for a transmission that Manufacturer specified to use Toyota-IV?
One of of the tricky things with this question is that googling "Aisin ATF Plus" does not return any hits for me. I suspect that it is a packaging for a local market or a counterfeit product.
Automatic transmission fluids are made to different specifications and many car manufactures use the same fluid. They just give them their own part number or marketing name. For instance my wife's BMW uses GM Dexron fluid, that makes it easy to find. In your case you are looking for T-IV fluid, you need to look on the multi-vehicle fluid container and see if it is compatible with T-IV. If not, DO NOT USE IT, because there are different incompatible fluids out there and you want to use something you know is good. There really are no multi-purpose fluids, it is just that most car manufactures use the same OEM transmissions under the covers.
As far as mixing new and old fluid, unless you are using a fancy flushing system you will not be able to get all the old fluid out. For instance the torque converter will hold onto alot of fluid. Again on my wife's BMW the recommendation was to change the fluid and then change it again after a few thousand miles. That way you end up with a good mix of mostly new fluid.
This manual specifies "T-IV ATF" and is noted in the table on the right, source