Replacing a fixture type within a show.

Depends on what the two fixtures are. If you're making a relatively simple change, like Mac 2K Profile to Mac 2K Performance, you can pretty much just change the fixture type and accept that you'll need to manually fix gobos and shutters - or if you wanted to be really fancy, you could use Query to swap everything out. Even between a VL2500 and a VL3500, you can at least get the basic positions, you'll just need to make a lot of manual changes. If you use a lot of by-type palettes, keep in mind that these will be messed up as well.

Alternatively, if you have more time and budget, the most effective way to do this is to lock yourself in a room with a model of each fixture and manually adjust each parameter to make the new show look like the old show. However, this takes a lot of time, and it's probably much easier to just wait and make these changes during tech.

Hi....

Having just done exactly this on a show, the critical things you need to be aware of are: 

- If you change the fixture type of a fixture that gets its palette information from 'by type' palettes, then all of the other fixtures of that type will lose their palette information through cues (ie. where they used to say 'L201' they will now say 'cyan30mag0yell0' or whatever. Fixing your cues therefore becomes very hard. If you use by-type palettes make them all discrete before you make patch changes.

- be sure your 'new' fixtures and your 'old' fixtures use the same attribute names, otherwise information can be lost. For example, a VL3000Spot fixture uses 'Zoom' for beam size; a VL3000 Wash uses 'Edge' for beam size. If you repatch the spot to the wash you will lose your 'size' information for all those lights in all the cues, palettes, presets etc (since you will now see a blank 'edge' attribute instead of the 'zoom'. The workaround is to make your own fixtures where the attributes match as closely as possible, or make custom 'changeover' fixtures that have both atts to let you copy the information to wherever you need to copy it to.

Check this carefully because even some fixtures that really should be the same are different in subtle ways (eg. some Vari-Lites use 'Col M Speed', others use 'Col Mix Speed'). 

- Eos ultimately seems to store DMX values for some parameters even when it presents them to you on the encoders as functions - for example, 'index' vs 'spin' mode for gobos. I can't remember the details, but if you imagine you have a VL3000 set to 'index' mode and you swap the light for a VL1000, the same DMX value means 'spin gobos quickly' in the VL1K. This can mean your lights are left spinning the gobos (noisily) in cues. The default values for strobe on VLs vs Macs also have quite markedly different effects!

Obviously once you've swapped lights you will then need to 'fill in' the correct information for positions, colours etc to suit the new light type, as others have mentioned. 

Hope that helps.

Rob.