Is there any way (with or without add-ons) to model and manipulate textures at the same time without UV-unwrapping https://twitter.com/joewintergreen/status/1262667173400506371 ?
No.
You have to unwrap in order to create a uv map for the texctures. No uv map, no textures.
maybe this is a different question then i think it is, but iâve textured without uv unwrappeing in every version from 2.39, up to and through 2.79, in textures using generated, and selecting cube or sphere as appropriate.
it was only in the game engine these didnât show up. but worked fine in rendering and animation with the old blender internal render engine. no idea what 2.8x does as i donât have the hardware to run it.
I remember trying to learn Blender on 2.76 and not realizing that I had to unwrap but I was still getting textures to show up on the objects even without doing so, but they werenât really assigned properly and would disappear later on.
Also, using nodes to create PBR textures is not the same thing since they only affect the material.
What the OP wants is a way to edit objects that are already textured so that he/she can extend the texturing to the new parts automatically, like shown in the link he/she provided. It could be done to some extant with PBRs, but you wouldnât be able to do much with it when it comes to finer texture details where bump maps or decals are often used in specific areas.
Yes and no.
You can make procedural materials what donât use uvs with box projection. But complexity of nodes what make good blending between materials and take account of curvature would be very high. Plus to make it all work at least semi real time without baking stuff⌠that would be very difficult.
You could try less complex approach by blending materials with vertex colors but thatâs more manual work (still no uvâs required). There was talk at last year blender conference what showed this method at 9:55 https://youtu.be/TkTQhmNFRnY?t=594
Here is example:
Blend file 17MB link
(textures from texturehaven)
If youâd look at my membership date, youâd probably know that I am aware of how it all works 
I edited the title of the thread, to make it a bit clearer.
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I edited the title of the thread to be less confusing.
UV maps are a must, because it going into the game engine (UE4). However, conventional unwrapping is not something I want to mess with because textures (preferably) need to be aligned and projected properly onto the newly extruded faces as I model (just like on that video from Half-Life: Alyx Hammer Editor).
Another case if perhaps I could model without unwrapping UVs first, but then when I do, Iâd like to be able to align textures (UV isles) precisely, on the grid, without spending a lot of time on it (basically a workflow similar to all old school BSP/CSG level editors).
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Everything you want to get out of Blender and into a game engine requires meshes and uvs.
If you want to procrastinate creating uvs till the end, use projected / generated Blender onesâŚ
⌠or you should be clever enough to auto-generate your uvs from the model itself, automatically. But that requires AI.
So⌠no.
I highly doubt that Hammer map editor has Ai that auto UV maps newly extruded faces.
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I tried something right now and while itâs a bit tedious way, itâs one of the ways to goâŚ
Basically, I selected a face, aligned view to the face, unwrapped face from view projection. Then I did the same thing to another face (adjacent to the first one I unwrapped, but tapered on one end) and then stitched both faces.
The problem with this method is that 1) pixel density is not maintained (tapered face was scaled larger than the first face I unwrapped) and thus when stitching or trying to align UV isles, texture on adjacent faces doesnât match and 2) each new UV isle is offset on the grid (UV isles are not on the same grid and texture doesnât align).
I think itâs gonna be faster to learn level design ue4-style or try find ue4 scripts what make bsp-style level design easier than to force blender as bsp-style level editor and then export stuff to ue4.
If you google âblender level editorâ you will find almost nothing and things what can be found are static mesh stuff, not bsp / csg.
UE4 level design style is making models in 3D app (like Blender) and mashing 3D models in the editor to make a level⌠Itâs not productive at all, especially for indies. Thatâs why you donât see too many levels like you saw in Quake 1/2/3/HL.
And no plugins exist for UE4 to offer Hammer-like level design flow (or Trenchbroom-like workflow for that matter).
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thank you yes, it was unclear. i had no idea half-life was being refered to.
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I donât know how to look up userâs information here. I just know how to try to help people because I like to try to help, not condescend.
Someone making addon for this workflow in blender:
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Hopefully he releases it to the public.
I think i can see what they do here but that require prepared textures as well. The basisc are still oldschool BSP workflows you can use in Blender with anything set tiling while using the world space coordinates.
But for the magic that get the face vs world size and apply the corresponding atlas tile, you need some shader math or a little script. But it still looks like regular world space mapping.
Maybe there is something you can âabuseâ from the certain Decal Projection addons for this purpose 
Edit: You can get some better search hits for âBlender level design tileable texturesâ that pops out quite a few interesting ones